I don't like checking in. For first, it lets everyone know where you are and when you are there. It creeps me for people to know exactly that - knowing when my house might be empty, or knowing when I'm at somewhere that is less safe. I also wouldn't like people knowing how often I'm out drinking or not out drinking.
I just feel like checking in is pointless. If you want people to know where you are, why not just tell them? Tweet about it. Update your status. Checking in is just another way to share information, I get that, but it's also a pinpoint on a map of creepitude.
It does kind of make me giggle when people have limited profiles or were previously the victim of stalking, but will use check-ins... It seems contradictory.
Do you check in?