I love Thunderbird. It’s killer features for me are quickfilter by text, quickfilter by status (the “View” dropdown), e-mail threading and auto-spamkilling, plus it’s just a nice solid mailer.
There’s one thing I’m missing though. In the “View” quickfilter dropdown, I’d like to be able only messages that are “flagged”. I use flagging to keep track of some stuff in one of my folders. Alas, although I can customize the filter by tons of other properties, flagging doesn’t seem to be included and it’s also AFAIK not one of the message headers so I could do a custom filter. So that’s one missing thing in TB – but that’s pretty much the only one.
UPDATE: apparently this is working in Thunderbird 1.5 (or maybe earlier too where I just couldn’t find it), see comments below. Great.