I'd join if it wasn't invite only, there are still some kinks with the SteamID system for it.
You know you can set it to private, rather than invite only. That way you can get applications from people whenever and then accept/deny them.
We have that on the work one ^_^ mainly cause no one could bloody join on the invite-only status. Remember the groups aspect is still a beta part of the community system.
I'm waiting for Valve to add achievements, cause then we'll have a pretty sweet Windows version of Live more accessible to everyone not just those with Live games. That's something that is irritating me atm, is there is no stand-alone games for windows live. You have to sign in either to xbox.com or via a game, just to check messages.
Going to probably sort out getting another account on Virgin; as they have a deal to have it free for a year if you're on or sign up to their broadband packages