[p01nd3xt3r]

Yes. I am currently working on one just for shits and giggles. Its called spotted.at http://spotted.at

The things that I am focusing on are

a) realtime b) not having to provide phone number c) valid listings (e.g.: listing disappears once item is gone)

[Skywing]

How do you plan on determining when an item has been sold or a listing has been "fulfilled"? The only way I could think of would be to make it as easy as possible for the ad's poster to mark the listing as expired, or something.

[veb]

I really love the idea with the map/location. Keep at it. :-)