Tried to send an invite and it's not there. Checked in to it w/ a google buddy and they are limiting invites right now. Said they'll be pushing more invites out in a couple days. I would say if you have it now feel lucky I like the rapid delete option for sure.
It pretty much just categorizes everything for you. Travel in one area, social in another, ect. I like it because of the mass amount of e-mail I never keep up on. During election season it's nice to have everything fall into one bucket and sweep it out.