Just to clear a few things up about Google's service. My school switched from Exchange to Google in Feb and we have been very happy with it.
Google does give you the ability to login to other user's mailboxes through a service called "OAuth", where, if enabled, you have a secret code you can use in the password field.
Some Google cons:
User manager for >250 users could use some work (no search option, only 30 users per page, etc.)
Sharing Documents does not allow sharing of organizational structure. So if you share 50 PDF docs, you can organize them into folders for each user
No mail folder sharing like Exchange, where we had Professors sharing certain mail folders with teaching assistants, now that is impossible.
Pros:
Spam/Virus is excellent!
We have students from 10 languages and all are supported
Google Apps Outlook Sync!
Uptime is great, the 1 time we had a problem they have a great site informing you of the problems and expected resolution
Great Troubleshooting/Help site with list of known issues and work arounds
Google Labs!
Once you get used to them, they are great: Labels, Conversations
Sync with ActiveDirectory/LDAP
Supported easily by mobile devices
There are probably more to add to each list, but those were the ones I thought of. Let me know if you have any questions about our experience with GApps. I can't really comment on the live@edu solution, though.
