Just parking a quick thought, but Google's Gmail strikes me as something of a bad business decision if it gets pursued in that fasion. They're going up against two deeply entrenched, well managed concerns (MS/Hotmail & Yahoo/YahooMail) on a service that people really care about (no errors allowed), and one that doesn't invite much innovation. Seriously, how much different is e-mail now from e-mail in 1994? Not much. They're also going to have a hard time getting bleeding edge types to adopt, since they're already heavily invested in some email application.
So I have a hard time seeing this beta move to being monetized, unless there's a huge draw that I've missed. Seems like more of a honeypot to attract users for more service experiments, e.g. contextual ads in a context besides Web search
Then again, they could always pull a WebFountain, and make it a service large corporations can adopt and use to get better knowledge management.