The invitation concept is interesting: Google corporate was able to generate a sense of scarcity when in fact none existed. Everyone wanted an address and you could only get one if you "knew someone". But now, I have 50 unused invites sitting in my account and I can't give them away fast enough.
Should Google decide to keep the signup process through invitation only, they'll have an interesting way to throttle future demand by giving out fewer invites to their existing customer base. Of course, they could do the same in a on-demand model by simply denying new signups but I imagine their reputation would take a hit that way.
From a tech perspective, I like the invitation model: Google could plan on no more than x users and throttle it up only when they were ready.
That said, anyone want a Gmail account?
Megan Golding
Work: Chrysalis Experiential Academy
http://www.chrysalisexp.org
Personal: Life With Rachel, one mom's Journey
http://www.kalamitykat.com