At that time email was validated, there was no doubt people wanted it, gmail was just better email. Contrast that to something like Wave which requires people to try something really new.
What could Wave have done better? explain why they need invites? Even better, expose their reasoning, eg they don't need to ease server pressure but they need quality signups? Anything fun I'm missing? Like skin-in-the-game moves from the private side, for macroscopic values of skin?
For Wave, I'd imagine they needed to publish data on which fun parts keep the new users returning ---there were MANY!
(So, we're both clearly not wishing to see their bugs from swiftly tilting these parts :)
