Actually this is the first sign I've seen that Google has actually learned some lessons from their failures.
First, this seems much more carefully thought out. The promotional material is beautiful, simple, well targeted and clear. Restraining from a full public launch shows they have learned from Buzz which failed in part because they got things wrong early and didn't correct fast enough. This shows a much needed loss of arrogance.
One other thing that makes it different: 500k Android activations per day. It will be very interesting to see if this gets pushed out as a default installed app to Android devices. Google never leveraged Android well to promote Buzz and I never understood why. Hopefully they won't be so shy this time around.
1. launch a social platform, but restrict signups to the point where nobody with access has any contacts on the service
2. keep it locked down until the buzz/hype is all gone
3. open it up to everyone and let them wonder why there was any buzz/hype in the first place
If they dont let early adopters use the platform and give the crucial early feedback, they might as well throw in the towel now.