I've started using Thunderbird again after months of trying literally every other solution on the market. I wanted to switch from Outlook and Gmail to something that is fast, has good keyboard support and a good message editor. It's incredible how slow most of the email clients on the market are. What's even more incredible is that, apart from Outlook, none of the other clients offer a good way of editing tables prop…
Out of interest are you hooked up to an Exchange account or IMAP? Exchange email accounts are the bane of my email set up at the moment.
I really like Thunderbird, but if you need to use exchange and are on linux I think there isn't a nicer option than Evolution at the moment. It plays nice with all MS services and integrates with the OS for contacts, calendar etc.
Ofcourse all of this only applies if you are using Linux and its possible evolution is annoying on non gnome systems (i haven't tried it outside of gnome). I think kmail also has exchange support but i haven't tried it.