Among those paying attention: Mail.com owner Jay Penske, who has just purchased Geller’s three-and-a-half year-old site, which averages around a million visitors per month.

Geller will be added to Penske’s growing stable of Web site operators, which includes high-profile gets like Hollywood power blogger Nikki Finke and celebrity editrix Bonnie Fuller.

Geller wouldn’t tell me what the terms were, but said the deal for his company — he’s the sole owner, and employs three writers — is worth “multiple millions”. If that sounds familiar, it’s because we heard similar numbers batted around when Penske bought Finke’s one-woman site last summer.

I assume the terms include an upfront payment, equity in Penske’s company and payouts triggered by traffic and/or revenue goals, so there’s likely a good deal of wiggle room in the deal.

In any case, it’s a nice bit of validation for a 23-year-old who never made it to college. Geller dropped out of Greenwich High School in Greenwich, Conn., presumably because he was too busy contributing posts to tech kingpin Engadget. He started his own site in October 2006.

Geller says he’s kept his name off of his posts, and off his site because it seemed like a good idea, “for marketing reasons.”

He will still keep his name off the site, but will be making a few changes under Penske’s ownership. Geller is changing the url to an easier-to-find bgr.com, for instance. And Penske will be bringing his own people to replace Federated Media, which has been handing sales for the site.

The content should remain the same, though: Plenty of stat-heavy posts about everything from Apple’s (AAPL)’s new iPhone (duh) to Research in Motion’s (RIMM) annual BlackBerry convention.

Yesterday, BoomTown was hanging in Hollywood at ContentNext’s EconCeleb’s conference, where I did an onstage interview with legendary editor Bonnie Fuller about the massive impact of the Internet on celebrity journalism.

With its instant ability to deliver news, video and more, sites like TMZ, PerezHilton, The Superficial and Yahoo’s (YHOO) omg! have become massive drivers of traffic on the Internet and–despite the saturation–the arena is still growing fast, especially among women users.

But for those not in the know about Fuller’s impact on how celebrity journalism has developed to its current power, she is the reason–more than any other modern editor–humanity now knows every move made by the unholy trio of Paris, Lindsay and, most of all, Britney.

As founding editor of US Weekly (with stints at Cosmopolitan, Marie Claire and other mags), and as the editorial director of the parent company of Star magazine, Fuller’s various editorial innovations–celebrities are just like us!–are now commonplace.

And like a lot of old media stars, Fuller is now working on her own new celeb-focused digital and media company, which she says is aimed at women 20 to 40 years old, plunging headlong into the Web arena.

Here’s my video interview with her in an alcove of the Roosevelt Hotel on Hollywood Boulevard, where we discuss what she is up to and where online celebrity coverage is going (Britney 24-7!):