Maybe lonelygirl15 needs to change her name to populargirl15. The online video program - which had a buzz-fueled debut last year thanks mainly to its presence on Google’s (GOOG) ubiquitous video sharing site YouTube - is now going to run on one of YouTube’s biggest rivals, News Corp. (NWS)-owned MySpace, as well.

MySpace announced Thursday that it has a deal with the creators of lonelygirl15 to run the show’s first season finale on MySpaceTV starting Friday at 8 a.m. The second season begins Monday and can be seen on MySpaceTV, in addition to YouTube and the program’s own Web site.

I spoke with Jeff Berman, the general manager of MySpaceTV, about the announcement Wednesday afternoon. He made much about the fact that the season 1 finale will be “exclusively” aired on MySpace in 12 snippets over a 12-hour period.

Still, how exclusive will the MySpace deal for the lonelygirl15 finale really be? As I reported earlier this week, a new British-based spinoff from the lonelygirl15 creators called KateModern is officially calling social networking site Bebo its home, but KateModern videos have quickly found their way to YouTube and other online video sites.

Berman conceded that MySpaceTV is really just offering a “window of exclusivity.” But he thinks that is enough to guarantee a large audience on MySpace, adding that the company enjoyed a successful launch of the show Prom Queen, developed by Vuguru, a company backed by former Walt Disney (DIS) CEO Michael Eisner with a similar strategy. Prom Queen originally aired on MySpace but is also available on YouTube, Veoh and Amazon’s (AMZN) Unbox, among other sites.

“You can see it on MySpace first or wait around and see it elsewhere,” Berman said.

Much has been made about the increased popularity of online video. But unlike television, there is little in the way of exclusivity. You can’t turn to CBS (CBS) if you want to watch Fox’s American Idol or an episode of ABC’s “Lost.”

Shows like lonelygirl15 and Prom Queen are fair game for scores of social networking and online video sites. That’s good for viewers since it gives them many options. But in many respects, the online video market is much more fragmented than the traditional network and cable TV business.

In TV, networks have identifiable shows that influence their ratings, which in turn, helps to set advertising rates. That’s not the case with online video. How unique is lonelygirl15 on MySpace if you can see the same thing on YouTube?

Of course, the biggest social networking and video sites, in theory, should generate the most interest from advertisers. As Berman quipped, “You have to fish where the fish are. Marketers care most about the ability to reach key demographics at key times.”

But Berman said he could not talk about plans MySpace had to generate revenue from lonelygirl15 or other online videos. He just cryptically said that, “there are very compelling monetization opportunities and we expect the market to mature rapidly.”

Still, until a real business model for online video develops, then the still infinitesimal online video advertising market may, as I argued last week, remain a small piece of the overall advertising pie for the foreseeable future.

So the only true lonelygirl of online video might be a woman in MySpace’s accounting department waiting for the ad revenue to start pouring in.