With GMail, if anyone has read my thread on the subject, you don't even need to use IMAP, because they've put in a hacked-up implementation of POP where you can get the same "benefits" - their server doesn't allow POP to delete messages and all mail sent via SMTP ends up in your INBOX, where it needs to be filtered back to your local "sent items" folder.

One big benefit of using a client-side piece of software is that you don't have to be treated to ads, nor do you have to have all your mail lumped into "conversations" aka threads if you don't want to.