How will Google prevent Gmail from being a storage depot?

Ever since the initial launch of Gmail, I've wondered how they'd prevent people from signing up for multiple accounts and using the service for high-speed, reliable, online storage, 1 gig at a time.

Need a place to put MP3 files? Big Powerpoint collections? Movies? Why not Gmail?

Lately I've been thinking that they might never open Gmail up for open enrollment; they might just stick to the invitation model. While that wouldn't solve the problem totally, at least it would limit it.



Just now I see that my stash of invitations has grown from the typical 6 to 50. Is this the real launch of Gmail? How many Gmail invitations do you see right now?

It would be fascinating to graph the pattern of Gmail invitations worldwide. I bet Google has the data from day one: who invited whom? Perhaps more importantly to Google: what mail service did they use previously? Hotmail, Yahoo, AOL...