Last week, I noted that Internet ad spending had dropped five percent in the first three months of the year, and wondered when Web ads might rebound.

And now, here’s a data point for optimists in the “soon, real soon” camp: Procter & Gamble (PG), the world’s biggest marketer, is pouring more into Web ads than ever. Last quarter, it increased its spending on Internet display ads by nearly 150 percent.

Those numbers, from ad tracking service TNS, via Ad Age, are similar to outlays from rival Johnson & Johnson (JNJ). Both companies are now spending about four percent of their ad bugets on online display–the boring banner ads on Yahoo (YHOO) and Time Warner online unit AOL (TWX) that everyone loves to complain about.

The numbers don’t include other Web categories like video and search. But as much as some of us (ok, me) like to chatter about video sites like YouTube and Hulu, Web video is still a tiny ad market. And  consumer packaged goods companies like P&G and J&J,  who bring you everything from toothpaste to diapers, have traditionally had less use for Google (GOOG) than other marketers.

These still aren’t huge numbers in the grand scheme of things: For P&G, that amounts to about $26.9 million in the first three months of the year; for J&J, $15.5 million.

But if this keeps up, it will be a big deal. Internet boosters have been waiting a very long time for the consumer packaged goods guys, who are responsible for a huge swath of offline advertising spending, to move onto the Web. Astonishing that it’s taken until 2009 to get them there, but you’re not going to hear many complaints right now.

Last fall, a small but vocal group of Twitterers managed to shame Johnson & Johnson (JNJ) into apologizing for one of its Motrin ads.

This weekend’s replay: a howl of outrage, amplified and directed via Twitter at Amazon (AMZN), which may or may not have instituted a boneheaded policy  regarding “adult” books on its site. Or “adult” books aimed at gay and lesbian readers. Or something.

What happened? It’s not clear. But search for “#amazonfail” on Twitter and you’ll find that many Twitterers believe that Amazon has stripped the sales rankings from all manner of books that deal with gay and lesbian, and/or “adult” topics, making them less likely to appear on the site. In essence, the Twittersphere charges Amazon with trying to hide material it finds distasteful or that it thinks some customers will find distasteful.

Example: Amazon’s listing for Annie Proulx’s “Brokeback Mountain” doesn’t have a sales rank. But the author’s newest book does have one.

From what I can tell, the meme started up on Saturday, but didn’t start building steam until Sunday afternoon, when I noticed mild-mannered types like New Yorker writer Susan Orlean railing about Amazon on Twitter.

And it’s still going. As I type this, after 10 p.m. Eastern on Sunday night, the “amazonfail” keyword is generating a dozen hits on Twitter’s search page every couple of seconds.

Amazon hasn’t helped its case by remaining more or less mute throughout the weekend. But, by Sunday evening, the retailer had issued the same line to me and several other reporters: “We recently discovered a glitch to our Amazon sales rank feature that is in the process of being fixed. We’re working to correct the problem as quickly as possible.”

Not a terribly illuminating response, and I’ve asked for more information. But no matter what really happened, Amazon now has a real problem on its hands: A vocal group of people believe the retailer has discriminated in some way against gays and lesbians.

When Johnson & Johnson got caught in the Twitterstorm last fall, it had a relatively easy way out: A profuse apology to people it had offended. But Motrin has a very specific customer base and Amazon has a much broader one, and anything it says or does regarding gays, lesbians and “adult” material of any stripe is bound to upset some people.

But the company should do the right thing and clear the air anyway.

UPDATE: Here’s an apology from Amazon, which doesn’t really explain what happened, but says the problem didn’t just affect books aimed at gays and lesbians.

The story: Big pharma Johnson & Johnson (JNJ) has rolled out a Web clip (below) in which a snarky, knowing commentator gripes about the social pressure to “wear” babies in slings, carriers, etc–and the Motrin-ready aches that “wearing” a baby can cause. And in the last few days lots of blogger/Twitterers have agreed that:

• The ad is offensive.
• Motrin/JNJ doesn’t “get” social marketing.
• Something should be done! Maybe a boycott.

How many bloggers/Twitterers are actually complaining about this? And are there enough to hurt JNJ, which made an estimated $1 billion in profit from Motrin each year? Mmmmmmaybe.

Tools like Google’s blog search and Twitter’s Summize search will tell you that, yes, some number of people are chattering about this on the Web. And as of 8:07 a.m. Monday, the Motrin.com site was down, whatever that means. But from what I can tell, only a few thousand people have actually seen the ad on Google’s (GOOG) YouTube. I’ve asked video watcher TubeMogul for info on the ad’s audience and will update when I get it.

But even if the outrage is widespread, it’s going to be hard make a connection between online chatter and real-world results. Otherwise Ron Paul would be the 44th President of the United States.

Meanwhile, at the risk of a cyber-stoning, let me say that I don’t think the ad–which seems to be aiming at the same set of people who buy very expensive strollers but feel a bit conflicted about doing so–is an outrage. And neither does the person who does most of the baby-wearing in my house.

I ran it by her in the twilight hours this morning, between feedings, and she shrugged: “It’s true.” Then she went back to sleep.

UPDATE: Twitter Moms unite! JNJ has apologized, and is very, very sorry. Kathy Widmer sends Forbes.com this mea culpa:

I am the Vice President of Marketing for McNeil Consumer Healthcare. I have responsibility for the Motrin Brand, and am responding to concerns about recent advertising on our website. I am, myself, a mom of 3 daughters. We certainly did not mean to offend moms through our advertising. Instead, we had intended to demonstrate genuine sympathy and appreciation for all that parents do for their babies. We believe deeply that moms know best and we sincerely apologize for disappointing you. Please know that we take your feedback seriously and will take swift action with regard to this ad. We are in process of removing it from our website. It will take longer, unfortunately, for it to be removed from magazine print as it is currently on newstands and in distribution.”

Lesson: Carping on Twitter does indeed work. Sometimes.