I second what Christina said! When I upgraded, I took the opportunity to clean out my styles and brushes and get rid of those that I don't regularly use. I think I still have more than most PSE users, as I use lots of brushes in designing, but I don't find that it bogs down too much, and I like the ease of having them installed already.
One thing that REALLY helped was to rename all my CU brushes, styles, and patterns, adding a "CU" to the beginning of the file name. That way all my CU stuff is clustered together and easy to find. :-)