For all those complaining that there aren't any major UI changes: who cares? It might be "under the hood" kind of stuff. Remember 10.2 introduced rendevouz (now bon jour) as a major feature, even though it didn't have any graphical changes to the OS.
There were several subtle changes to the UI between 10.1 and 10.2. But the BIG story with Jaguar was Quartz Extrememade OS X a lot faster of any system with an AGP graphics card.