foursquare is a cross between a friend-finder, a social city-guide and a game that rewards you for doing interesting things. We aim to build things to not only help you keep up with the places your friends go, but that encourage you to discover new places and challenge you to explore your neighborhood in new ways.
Basically when you go somewhere, you "check-in" from your mobile phone or laptop and you let your friends know you are there, like: restaurants, parks, etc. You can also add a to-do list and tips for the place you are at. It's pretty neat. You also get "points" when you check-in to places.
Do I think it's necessarily the safest thing? No. It does have your current location on it (just the city) and lists the latest place you have checked-in, so someone could know where you are.
#1 safety tip for foursquare I have come across:
Check-in when you're on your way out so no one really knows you are there and they can't actually find you when you are there.
I have had a foursquare account for a few days, but just started using it today from my BlackBerry. I have checked into three places, as of now, and am just kinda checking it out still. I have added a few things on my to-do list, like a few local restaurants I would like to check out, and have left a few tips for people to see about my favorite places to go.
I do not think this is super popular yet, but I think it will grow. As a society right now, we are all about ourselves and we like to let people know what we're doing at all times. That's what the "immediate" update we have going on at all times is about. There are thousands upon thousands of feeds on Twitter telling us what you are doing 24/7. Does anyone actually care? No, but we like to think someone does.
So this thing with foursquare... it is original? Kind of, there are other things like this. Do people really care where you are? Probably not, but there is a chance you could see that a friend is at the same place as you. Plus, it is fun to "check-in" and "get points." I think it will be around for a while and gain popularity quickly.
Check out my foursquare: http://foursquare.com/user/laurenkgray
Foursquare definition from: http://foursquare.com/help/