Valve has publicly launched Steam's community features after a brief beta test, meaning that when you next log on your kit will be updated.
The community stuff adds an Xbox Live-style in-game layer (accessed by pressing Shift-Tab), which allows you to converse with your friends, change your name and all sorts.
Your unique Steam ID (like a gamertag) is also accessible via the net, so you can set up a page with your picture and that, and view all your play statistics, and ask yourself why I've spent so long playing Doom 3 recently when I could have been playing through BioShock for the third time.
All in all, it's quite interesting, and comes online just in time to ease the introduction of next Monday's Team Fortress 2 beta - available to people who pre-order The Orange Box on PC.