It's simple: because I hate how much of my life Facebook already owns and has control over. Facebook is now worth $33 BILLION--all because chumps like me are willing to share their lives with the world and Facebook gets to sell us out. Why the hell am I going to give them one more piece of myself to monetize for their own gain?
I've said it before and I'll say it again: I have a love-hate relationship with Facebook. It makes it easy for me to see what's going on with friends, family, plus hundreds of people I don't know and/or don't care about on a daily basis--I'll grant it that. It's also a nice business tool (if you don't mind having to monitor your pages 24/7 and sleuth out changes on your own since Facebook doesn't communicate with nonprofit Page admins AT ALL). But I hate how little control we have over Facebook--privacy stuff, the way they constantly change the way information is displayed, the total dearth of features for Page admins, the fact that the "like" button interface sucks...I'll spare you the rest of that rant.
As for the whole checkin thing, I'm still on the fence about it: it's bad enough I spend time doing Foursquare, which so far has been of little or no use to me; there is no way in HELL I'm going to go to even more effort and trouble to check in using Facebook Places. I'll be interested to see if Places takes off or falls flat on its face.
How about you--have you tried Places yet? Or are you intentionally steering clear of it like I am?