The question is what has prompted you to switch back? Is it something you are not getting from Thunderbird that you would otherwise be getting from Outlook or Outlook Express?

I tell you what I don't like about Outlook/OE, it's the fact that OE gets tied in with Internet Explorer and Messenger too much. I don't want my mailing software to come with strings... that said, I use OE most often.

Further OE hasn't been updated in quite some time... which sucks. Microsoft tend to piss all over tools that they offer for free... and they don't add much to those tools very often.

Thunderbird gets updates more regularly AFAIK.