Steve,
I've been using it for years, it's wonderful, has lots of extra extensions and themes, tabbed browsing is great once you get used to it, all in all just a much better browser than IE ... and besides, it's not microsoft ...
And "Thunderbird" is a dynamite mail program. If you need all the bells and whistles of Outlook (Calendar, Contacts, etc.) that's another story but if your using Outlook Express, it's worth changing to Thunderbird.
Keep Smilin'
John