My not quite famous enough 5 – #4
I'm not that keen on Lightroom 2's new Filter Panel, as I said here. When I do use it, it's usually because I want to temporarily filter the visible items down by key such as rating or sometimes by masters or virtual copies - ie by one of the old Lightroom 1.4 filters.
Display the Filter panel for this purpose and you lose a very prominent chunk of screen space, where your pictures belong. Then you'll eyeball which iTunes-style columns are already visible, perhaps wait while Lightroom starts chugging through populating and counting them up. Clear whatever filter is already present (not an issue for me as I never use the Panel) and then click “Attributes” to set your filter on rating, colour or whatever. Now that's a bit of a palaver, isn't it?
So the fourth little gem is that you can save these Filter Settings. I'm currently running with about a dozen of these, and always access them through the Filmstrip. Some will actually configure the Filter Panel as I might want, but mostly they're for those important things like ratings. If I want anything fancier, it's Smart Collections.