Show Favorites as a bar in the UI with button 4 ea. favorite
This would be very powerful.
If you just had a bar across the bottom of the tree with a list of your favorites, with each favorite being a button, you could make them all filters, etc.
That would give you FAST access to the most used filters AND shows you which filter is currently applied.
Uorganized does a very very nice job with this. Check out their screenshot. The filters bar has a button for each type of filter. And the applied filter is highlighted.
http://www.veetosoft.com/images/ss/complete_big.jpg
They also allow TWO filters and TAGS to be applied. Very powerful yet easy to use.