From the website:

Socialight is a fun, new community that lets you connect in totally new ways - by creating, sharing, and discovering virtual Sticky Notes placed at specific locations using your mobile phone or the web. Socialight is about location-based information. Geeks call it "geo-tagging". With this service, you can create Stickies anywhere in the world for your friends, for everyone, or just for yourself. They can now contain text and photos, and soon you'll be able to add sound clips and video.