I used Foursquare, and I never found it more interesting than just a tool to check-in. And I see no value in that, nevertheless, I still felt LBS is a gold mine yet to be properly mined. And I'm determined to solve this problem! Or the problem of trying to trying to find interesting things around you. (Which is by itself a really different problet FS seems to be solving)

And I'm solving it on the very promise that people don't care too much about what strangers around are doing, but would however be way more intrigued to find out what their friends have done in the area.

Here comes in ctrleff! (ctrleff.com :X sorry for shameless plug) I'm a solo founder and things are going really smoothly! I hope to see something launched soon! And naturally, HN will be the first place I'd seek feedback from.