Doppelgangers?

I don't really understand this whole "doppelganger" thing on Facebook -- but suddenly all my friends' profile pics have been replaced with Celebrities. One of my councilman friends is now William Hurt, for example. One of my writer-buddies is Hunter S. Thompson.  It's kinda entertaining.

I'm not sure if their "doppelgangers" are supposed to be people they look like.... or people they want to look like? I mean, I know what a doppelganger is; I went to college and all. But it's my recollection that seeing one is bad luck, so I'm not sure I should even play.

I just went through and picked two women I'd like to be when I grow up -- Bonnie Hunt and Amy Sedaris. The only plausible resemblance I can find is that they're also blonde and frequently wear glasses. Who doesn't love a smart funny blonde? (That's my story, and I'm sticking to it.)