Its almost certainly going to be purely personal storage for a number of reasons, two of which are:
1) It would be a bad thing[size=9]tm[/size] for the world to be able to see into your mailbox (They could solve that by having some folders hosted and some not I guess, but then the gstorage stuff is unsupported by Google as far as I know, and not really what the service is meant to be used for.)
2) Cost - Google are trying to run an email service, not the worlds biggest free hosting service. Imagine the bandwidth implication of everyone looking at my junk email attachments, and me looking at everyone elses.
You say that, but look at google calender, but yeah understand what you say, thanks for the info.
gspace is nice though to stick things on there, the mail you get is cool.