Might want to review the Terms of Use.
[link|http://gmail.google.com/gmail/help/terms_of_use.html|Terms of Use].
I think they want you to put lots and lots of e-mail there. E-mail that they can do various things with to increase the relevance of their ads.
I think using it as a file system violates their terms, though many people do that. Similarly, I don't think they'd be happy with you sharing your account.
I've got an account there too, but I've done almost nothing with it. (I've got 1 piece of mail in the Inbox, and 1 in the Spam.)
I assume that ultimately they'll let people do things like use it for personal web pages, etc., probably similar to Apple's iMac stuff.
FWIW.
Cheers,
Scott.