I use it its ok i guess.. its set up nice and you can also show where ur at on ur facebook wall its not bad. You aslo win badges for things like 3 stops in 1 day and ect.
I think the privacy concerns for FB/4[] are ridiculous 99% of the time. Seriously, it's not like people can't see you where you're at, and if someone is stalking you (as a general rule of common sense) you probably don't want to let them follow you on either service, or talk to them, or anything similar.
Oh, and to the OP - I have 4[]. it's kinda nifty, but tbh I rarely use it - it's kinda pointless unless you have a bunch of friends that use it too (think high school )