Some people are reporting that Gmail is introducing IMAP support. This is a real bonus for those of us that want to access our mail on the cloud while at the same time maintaining a synchronised offline copy.
My current system for handling Gmail is to download it all through POP3 (and keeping a copy on the server). Email that is sent from my Thunderbird client goes through the Gmail SMTP servers which save a copy of the mail in my sent items "folder".
While this works, it's not as good as real IMAP. It looks like Google are making some web UI improvements to Gmail as part of the upgrade and although I don't have this feature yet, it looks pretty promising.