If you are going to use a tree view for something please consider reducing the horizontal white space that creates the indentation in the tree. Instant messenger buddy lists, for one, use too much indentation thereby meaning I can't shrink the window very much and see more than 2-3 characters of the name. The WMP tree view is also guilty of this. Its worse there since the tree is guaranteed to be several levels deep depending on the path you take into your music collection. You have to use a scroll bar to navigate left and right just to get around the tree.
I guess I just think that most people don't need all that indentation to know they are at a different level of the tree, but I must be weird, because we've been stuck with space hogging trees for a long time now.