On a side note, the ability to hide a community from the rest of the portal users would be nice as well. I think it might help with security.

It would also be nice if only the portal owner (and maybe a designated admin) would be allowed to let new people join.

I frequently colab with actual physically separate companies and it wouldnt be a good idea if I could just join up in their communities =) I think that the org of LR with communities, organizations, and adding "sites" is great. Its probably just the beta version I know...

I have to say tho that I am so impressed with it that if anytime you guys/gals are in Seattle, Im buying the beer!

Ryan, we've added private sites to the next release.

Perhaps you can make a feature request for being able to enable or disable user-driven sign up.

http://issues.liferay.com/browse/SOS