Facebook runs the risk of being exposed as a "fad," Microsoft CEO Steve Ballmer told The Times Online. The jab calls into question rumors from last week that Microsoft was eyeing an investment in the social networking site.

"I think these things [social networks] are going to have some legs, and yet there's faddishness, a faddish nature about anything that basically appeals to younger people," Ballmer said.

Fads aside, social networks have gotten a lot of attention from major internet players. Google, which also has been rumored to be interested in Facebook, has Orkut. Meanwhile Yahoo! looks to have given up on its Yahoo 360 network in favor of Mash, which the company hopes will be a bona fide threat to MySpace.