I've been revising my own email-storage strategy from being a mix of server-side folders via IMAP and local mbox-files (Thunderbird) to having all email stored on seperate Google Apps accounts and a Google/Gmail account to serve as a central archive for all external accounts. (on top of this I make my own backups from Gmail, of course)
What kind of setup are you using? (this applies to both ISPs as well as individual users and companies not directly involved in the hosting business).
It'd be interesting to discuss this topic, as I think it is something that is crucial for everyone's information handling.