Gmail via IMAP!
I’m a happy man. Now that Google has added IMAP access (Google is rolling out IMAP over several days; it’s possible that not all Gmail users have the option yet), I can see my Gmail messages from Outlook, Mac Mail, and Evolution (my email clients on Windows, Mac OS, and Ubuntu respectively) and move messages back and forth from the school’s Microsoft Exchange server to Gmail, effectively making Gmail a gigantic back-end store to my more limited Exchange account. Gmail labels are mapped to IMAP folders, so moving back and forth between Gmail web access and IMAP access very natural.
Here are some links for configuring Mac Mail and Outlook It’s not hard to find Google’s instructions for many other email clients.