Turns out that many of them were doing the same thing–the Facebook part, that is. Web traffic-watcher Hitwise says Mark Zuckerberg’s site accounted for 1.93 percent of all U.S. Internet visits on New Year’s Eve. That’s up 75 percent from a year ago, when 1.11 percent of you checked in at the site at some point in the day.

But New Year’s wasn’t Facebook’s busiest day last month. That distinction belongs to Christmas Eve, when it set a site record of 2.18 percent of U.S. Internet visits, up from 1.42 percent in 2007.

You can draw your own conclusions about what those stats mean, or read Hitwise analyst Heather Hopkins’s theories here–she thinks snowstorms in the Northeast kept people trapped in their homes with nothing to do but post on their pals’ walls.

But I think the best explanation here is the simplest one: Contrary to predictions that Facebook would burn out as its core college audience grew tired of it, the site has continued to grow–it now claims 140 million active users worldwide. So you’re going to see records like this broken a few times a year.

So what does that mean? Nothing, really: Assuming the data are accurate, we still don’t know what people actually spent, and what they spent it on. We’re likely get a few more pieces of the puzzle today, when/if comScore (SCOR) comes out with its online commerce numbers. But the most important data are still locked away in retailers’ databases, and that stuff won’t be public for some time.

[UPDATE: ComScore says sales were up 15 percent.]

One way to tell how retailers really did: Ask somebody who sells Web advertising. An ad exec for an online publisher I spoke to yesterday told me that December sales had “stopped cold” because his clients wanted to see what their Black Friday/Cyber Monday numbers looked like before committing any more ad dollars this year.

He’s hoping for good news. As of last night, he hadn’t heard a peep.

In the meantime, here’s an array of data points from Nielsen and rival Web measurement firm Hitwise. Here are Nielsen’s top online retail destinations, ranked by unique visitors. Note the big increases at Amazon (AMZN), Best Buy (BBY) and Sears (SHLD). Why is Netflix (NFLX) considered an online retailer? Got me. (Click to enlarge)

And here’s Hitwise’s summary of Cyber Monday; note that its take on traffic seems to differ from Nielsen’s when it comes to overall visits:

• Among the top 500 Retail Web sites, the percentage of U.S. visits was down 1% on Cyber Monday 2008 compared with 2007.
• U.S. visits to Brick and Mortar store Web sites (100 total) were down 4% on Cyber Monday.
• U.S. visits to Online-only Web sites (100 total) were up 5% on on Cyber Monday.
• U.S. visits to the Comparison Shopping Web sites were down 21% on Cyber Monday.
• U.S. visits to the Catalog Web sites were down 4% on Cyber Monday.
• The top visited Retail Web site on Cyber Monday 2008 was Amazon.com, receiving 10.77% of U.S. visits among the top 500 Retail Web sites. Walmart.com was the second most visited with 8.55% of visits, followed by Target.com with 4.56%. BestBuy.com was the fourth most visited with 3.81%, and Sears.com was fifth with 2.74% of visits.
• Amazon.com’s traffic increased 21% on Cyber Monday 2008 vs. 2007. Walmart.com’s traffic increased 6%.

[Image Credit: Respres]