YES. I've wanted this for ages. 8)Saved Search Folders display messages based on previously set search criteria. For example, instead of filtering messages into a new folder, you could create a Saved Search Folder that lists all the messages received from a certain person over the past 30 days, even if those messages are stored in different folders and subfolders.
Thunderbird is my everyday email client and I have absolutely no complaints about it. It's been installed since .5, became my default by .6 and has never let me down since. I'd recommend it to anyone. Just can't wait for 1.0. 8)