I've been using Lookout for awhile now. This is a must-have productivity tool for Outlook - and about the only efficient way to search your e-mail if you're not using GMail.
The experimental version supports search restrictions (as of a few weeks ago). As you can imagine, this is a pretty powerful feature. I have a number of restrictions to search only sent items, mail sent directly to me, and all subscriptions (RSS and mailing list).
All in all, it's been pretty stable. If you're running any older version, I highly recommend the upgrade.
My only real complaint with Lookout in general is the search results window. The only thing you can currently do with an item is open it.
It would be infinitely more useful if I had the ability to “open the containing folder” and delete the item right there. (Ultimately, I'd love to be able to drag to a different folder or even have the reading pane to the right, but I'll settle for delete for now).