The dancingmango has a great post on how he made the UIs in his PowerPoint presentations look like they were drawn by hand. Why would you want to do this? Often when someone not directly involved in day-to-day development of a UI application sees a great looking UI in a doc/slide/demo/etc they assume the development is almost functionally complete. Keeping it ugly is a useful tool to help manage their expectations.
One trick I used to use with Swing applications was to switch the UI skin to the ugly default "metal" look and feel for the demos done during the initial UI development stages, then switch it to the "windows" look and feel towards the end stages of the development.
I wonder if there is an ugly switch for .NET (WinForms)? Should be easy to do an ugly css (plenty of ugly wesites to get ideas from :)).