Socialight

Socialight is a cool looking mobile2.0 app that lets you create 'sticky notes' at a real-world location that are accesible on a mobile phone.

You leave your message (picture, message, sound..)in space via your mobile or the Web. When people running socialight are at that location, they can see (or hear) your sticky-note.

Looks really interesting, but at the moment it appears to be US only.