While using Vista, one experiences programs that expose Vista controls. Some others show XP-ish controls, while some others still look a lot like Windows 95/98/2K and, still, there are others that break away completely (Office 2007, Nero) and present a completely different user interface with weird shaped windows and menus that look like nothing else in the OS.

OSX is somewhat better organized, but, still, programs, even Apple ones (Safari? iTunes) have a variety of looks that get presented without much coherence. Apple is too guilty of this.