To add another layer...
I run my own mail server on a NetBSD box (a P150 for those who care). I run an IMAP server and connect via Mail.app (or Outlook Express in the bad old days). The beauty part is that I also run a php based webmail server called IMP. The upshot is that since IMAP manages mailboxes on the server I can connect via Mail.app, view mail, move stuff around, create and manage folders, etc.... Then, when I'm on the road, I can pop open a web browser, head to my webmail page and see all my folders and messages from anywhere in the world. Because both Mail.app and IMP use IMAP all my folder management changes are reflected in both places. If that weren't enough, I can also ssh into the machine and simply use PINE (mutt, elm, etc...) since the mailbox format is identical. PINE is actually what I end up using more than anything, but it's the flexibility that makes this solution rock so much.
Just trying to keep things as complex as possible....
-alex.