1) Too many people I don't want in my "face." I don't want people I work with in my "social network." I don't want my family and family friends seeing the profiles of my kooky New York friends. Facebook is mixing too many worlds. Good for FB's # of users bad for me.
2) Agressive ads. I hate the Volvo ads in my news feed. I hate the newsfeed JPeg of Gwen Stefani with the caption, "Hey, want to help me design something cool on HP.com?" [It's funny though, they can't target me that well because I didn't select a gender so I get neutered ads.] With their total costs-to-ad sales ratio I think they can make some effort to not be complete ad-whores when their users are their only real asset.
3) I've outgrown it. The fun of Facebook was the photos and finding people and there doesn't seem to be anyone I want to find or stalk so, where can I get an online network that is basically an online switchboard where you friend people you know and have access to people you've already friended?
4) It's getting creepy. I'm talking about the Boomers. With all these companies joining and old people sending each other martinis - it's becoming a strange massive reunion where a VP at my company probably sees when I friend someone or change my status. One Boomer agrees - read Daniel Lyons "Party Crashers on Forbes.com" (not available on FDC *!#*@ so refer to the Globe & Mail who republished it)