That is almost certainly a record for a Web-only event. But it’s a nonevent by mainstream entertainment standards.

A poorly performing show on network TV, by comparison, draws millions of viewers: Recall that GE’s (GE) NBC canceled “Quarterlife,” the soap opera that started out on MySpace, after it drew an audience of 3.1 million in its debut. A bona fide hit draws many millions more: Last Thursday’s episode of “CSI,” for instance, garnered more than 18 million eyeballs.

Not fair to compare a weeknight audience to one on Saturday nights? OK. Try this: Last year, before anyone had ever heard of Sarah Palin, “Saturday Night Live” was averaging more than five million viewers.

You can’t blame the modest audience on a lack of effort on YouTube’s part. The video site generated plenty of publicity in advance of the event. And heavy promotion on the site itself all but compelled visitors who ventured onto YouTube last night to check it out.

Part of the issue, I think, is that while the show had a smattering of sort-of-popular singers (Katy Perry, Akon) there was no one really huge. Most of the show was dedicated to viral video stars/oddities like Tay Zonday. And the point of viral videos is that you see them on your own time, serendipitously: You take a couple minutes out of work on a Tuesday afternoon to watch Tay Zonday sing “Chocolate Rain” because your friend sends you the link. Not because he’s appearing live on Saturday night.

Could YouTube rustle up a bigger audience for a live event in the future? Absolutely. It’s one of the biggest Web sites in the world, so if it had a truly compelling show, instead of a niche event, it wouldn’t be hard to get the word out. And if parent company Google (GOOG) wanted to lend a promotional hand, game over.

So maybe that’s coming down the pike. In the meantime, if you didn’t tune in last night, here’s a sample of what you missed: Katy Perry singing “Hot ‘N Cold.”