I like the revised Mail.app (though judgement still reserved on the TODO’s and Notes features). One thing I have noticed is that you can now do Gmail style searches in the main search bar.

Keywords that I’ve found work so far:

from:

to:

subject:

Haven’t worked out how to do date based searches yet, and folder: or mailbox: don’t seem to work yet, but I’ll post more if I find something.

UPDATE

I found some more in the spotlight searching help file

date: eg date: yesterday or date:24/08/07

kind: eg kind: document or kind:movie (this find messages with an attachment of a particular type)