Analyst Imran Khan says he talked to 20 ad buyers and planners, who control a collective $1.6 billion in ad spending, and they tell him that they’ll spend more in the second half of 2009 than they did in the first six months. But that’s not useful information, since ad spending is traditionally weighted that way.

More tellingly, Khan’s correspondents tell him they think spending will be “roughly flat to down” in the last six months of 2009, compared to 2008. And as we’ve discussed before, ad spending started plummeting in the second half of 2008. So if it isn’t improving now, that’s unpleasant news.

More pleasant: Things should get better next year:

2010 ad budgets are looking positive. 25% of respondents see upside of 5-9% in 2010 and an additional 25% see upside of 10-14% vs. 2009. Approximately 40% think that ad spend in 2010 will be roughly flat with 2009 levels.

Looking for more concrete data? Wait a week. Earnings season kicks into high gear Thursday, Oct. 15, when Google (GOOG) hands in its Q3 report card; in the following weeks we’ll also get updates from big media players, including Yahoo (YHOO) and Time Warner (TWX).

But here’s a very slight twist: The sales decline slowed in the most recent quarter. U.S. sales dropped 11.1 percent in Q3, compared to a 14.5 percent drop in Q2, according to Nielsen Soundscan.

That’s the good news. The bad news is that Michael Jackson isn’t going to pass away again–and that unless they finally do come to Apple’s (AAPL) iTunes, there probably isn’t another way to repackage the Beatles again. Billboard:

Renewed interest in the Beatles and Michael Jackson slowed the decline of U.S. album sales in the third quarter, although the industry is still on track to fall for the eighth time in nine years….

Music retailers are hoping that the continued performance of Jackson and Beatles albums and a strong fourth-quarter release schedule will continue to make up lost ground.

During the quarter, Jackson’s June 25 death fueled sales of about 5 million units, and the September 9 re-release of the Beatles catalog has sold 1.3 million units so far.

So far this year 11 albums have topped the 1 million-unit mark, the same number as in 2008. In 2008, the top seller was Lil Wayne’s “Tha Carter III,” at 2.5 million units; this year’s top seller is Jackson’s “Number Ones,” at 1.8 million units.

ComScore says Twitter logged 30.1 million search queries in May, more than Time Warner Cable (TWC), but not even on the same playing field as search also-rans like Ask.com.

But what if comScore is dramatically undercounting Twitter’s search–not just the standard undercounting that Web publishers always complain about, but something more significant?

It’s a given that comScore is undercounting. I know this because the research outfit told me so: The company confirmed today that it only measures searches executed at Twitter.com. But at least half of Twitter’s users are accessing the service without visiting the site, via third-party clients like Tweetdeck. And within that group of users is the power-user set, which is far more likely to be executing searches, many times a day in some cases, than Oprah fans who just joined the service last month.

So it’s easy enough to conclude that the majority of Twitter’s searches are going uncounted by comScore (SCOR). But how big is the gap? I’ve asked Twitter to share its search numbers, but I’m not holding my breath on that one. (UPDATE: See bottom of post)

In the meantime, let’s do some guesstimating.

Start with this year-old post by John Borthwick of Betaworks, who at the time was an investor in Summize, a Twitter search engine at the time (Twitter later bought Summize outright).

Borthwick reports seeing a huge number of search queries on Twitter on the opening day of Apple’s (AAPL) 2008 developer conference, topping out at an average of 190 queries per second. Tease that out over a full day, and you get 16.4 million searches in 24 hours.

For argument’s sake, let’s say that most of those searches occurred in an eight-hour stretch before, during and after Steve Jobs’s pronouncements that day, and knock that total down by two-thirds, to something like 5.5 million queries.

Steve Jobs pronouncements are rare things so it would be wrong to assume that Twitter sees similar usage patterns every day. But then again, Twitter has had an insane growth spurt in the last year: The most recent comScore traffic numbers peg monthly visitors at 32 million world-wide, up from a couple million a year ago.

See where this is going? Again, for argument’s sake, let’s say that Twitter’s peak traffic a year ago is now close to daily traffic today, and extrapolate that 5.5 million query guesstimate out for a month: You get something closer to 165 million queries.

Want to tweak any of my assumptions above? Be my guest. But no matter how you cut it, I’m sure that Twitter’s real search numbers are going to be several times higher than comScore’s number, at the very least.

Again, this matters in the end because Twitter’s most compelling investment thesis is that it can provide real-time search. And for that to mean something, the company is going to have to start registering as an actual search competitor at some point, not just to Time Warner Cable but to Yahoo (YHOO), Microsoft (MSFT) or even Google (GOOG). So how close, or far away, is that from happening?

UPDATE: Twitter cofounder Biz Stone responds, but declines to hand out any numbers. No surprise. I am a bit surprised to see him play down the importance of search at Twitter. I wonder if his investors are also surprised.

We don’t share absolute data such as total requests or queries per day but we do look at the whole ecosystem when we measure these things (not just Twitter.com).

Also, we are focused on the sharing and discovery of tweets so comparing Twitter to web search is interesting but not necessarily how we would measure success.

So says ad-tracking firm TNS Media Intelligence, which pegs the slump at 9.2 percent for the last three months of the year, compared to an overall drop of 4.1 percent for all of 2008.

I’m sure that someone, somewhere, will get some benefit from knowing exactly how terrible the ad market was several months ago–we also know, for the record, that ad sales were very bad during the first three months of 2009. But every media person I talk to is consumed with the state of the market right now–and what it might look like six months from now.

The good news: Some of the people I’ve talked to recently actually have good news to report. Or at least, good news as measured by the standards of  the “down six percent–or 20 percent–is the new flat” era.

For instance, execs at big Internet publishers tell me they think the decline in display ad spending may have bottomed out last quarter, which would bode well for restructuring efforts at wounded giants like Yahoo (YHOO) and Time Warner’s AOL (TWX).

Cable executives are even more bullish, and some of them, like Viacom (VIA) CEO Philippe Dauman, will even say so in public: “Signs over the last weeks have been encouraging,” he ventured during the company’s earnings call on Friday.

Let’s be clear: Viacom’s U.S. ad revenue dropped nine percent in the last quarter. So “encouraging signs” doesn’t mean “roaring growth.” And some moribund industries, like the magazine business, are still moribund (and broadcast TV’s day of reckoning is coming this month)

And even this faint optimism may be nothing more than delusion fueled by the stock market’s recent run or the hopes pegged to the notion that people have to start buying cars again, some day. Assuming the recession/depression lasts for another year or so, you can expect the ad market to really recover a good six months after that, since ads are a trailing indicator. But they do have to come back, some day. Right?

J.P. Morgan’s Imran Khan does some quick math and concludes that what Time Warner (TWX) is really saying is that ad revenue at AOL dropped 18 percent in the last quarter (see below for math). That’s awful, but believable: AOL ad revenue dropped six percent in the previous quarter, and as I noted last fall, those results only included a couple weeks of flat-out economic collapse.

This obviously doesn’t augur well for the rest of the Internet ad business, either. But only the most die-hard optimist thought that the Web was going to survive this thing unscathed anyway.

No comment from Time Warner on Khan’s math. We’ll see actual numbers Feb. 4, when CEO Jeff Bewkes announces the company’s year-end earnings results.

Khan’s estimate, from his note:

“We estimate that advertising revenue shortfall at AOL is at least $64M implying an 18.4% Y/Y advertising revenue decline. We make the following assumptions to arrive at this estimate: (1) we assume that half of the 1% shortfall in Y/Y Adjusted OIBDA growth that TWX press release attributes to both Publishing and AOL is due to online ad revenue shortfall; and (2) we assume a 100% incremental margin.”