These limited closed betas seem to really kill hype on a lot of their products, which leads to them not having a lot of use, then google killing them...
To be fair, the beta, invite-only status of GMail was, at the time, the definition of Internet Cool.
It didn't work out so well when they tried to reproduce that success by making Google Buzz invite-only. My feed consisted of a few people posting "buzz!" and then never posting again. Google+ was similar.