Google+ is currently running in limited beta by invite-only. savesomesilence may have an invite to send you.

They need to get a feel for what the capacity will eventually be and get immediate feedback on what's good, what's bad, where the bugs are and if anything needs to be added to improve it.

Facebook's major issue is that they are forever changing their interface and people are done with it. They want a site that will reliably always be something they can easily use and enjoy without having to figure out 100 new features every month.