Facebook sort of did that too, by allowing only college kids at first. I think it's the right idea. It only became stupid with Wave when they started giving out millions and millions of "invites". At that point they should've simply made it public.
But really, Wave was a fundamentally flawed project for multiple reasons: bad market fit, clumsy/complex UI, bad marketing, etc. I had a bad gut feeling about it since I saw the demo (which took 1 hour! That should've been a sign)
Google+ looks very exciting and it seems like they've addressed many issues social networks have had through out the years, including Facebook. The lack of a Circles like feature was a design flaw of all social networks so far, and I believe it led them to ultimately become irrelevant because of the sheer number of people that became your "friends" on those social networks, which ended up spamming you. Circles seems to fix this, and the other Google+ products looks awesome, too.