If you have "hacked" your Vista to use a custom skin you surely know this problem:
An app tries to look like your current theme, but as it doesn't know that "My cool hacked theme" actually is "Aero Glass" it looks terrible.

If you have this problem with one of your own WPF apps, here is a nice solution (uses reflection): http://blogs.windowsclient.net/ricciolocristian/archive/2008/11/07/real-force-theme-on-wpf.aspx