The guy who built my computer for me installed Office 2007, so I do occasionally use Outlook 2007. It's much more email client than I need these days, but since it's already installed I saw no reason to go for T-Bird or Windows Live or something. So, I have my (MyOpera, Live, FastMail, OpenMail) accounts set up on it and have a number of Gmail-like color categories for all my mail so that it's reasonably well organized (though it really doesn't need to be organized
that well, since the search function works great !). I use it mainly for an offline backup so I don't have to trust my email to online storage. I don't use it too much for reading/writing, since I'm finding it impossible to change the Mail & RSS reading font away from the default Calibri to something else.
I've also been using Opera browser more and more recently and have enjoyed using its built-in client for both mail and RSS feeds.
That gives me two offline back-ups of mail.