I was prepared to be unimpressed as my present version of OSX works beautifully. This morning I downloaded and watched the 30 minute video on the new Jaguar OS. Damn! Great changes to Mail and all file handling. If there is a reason to buy Jaguar, it's probably "Time Machine". It automatically backs up files to a peripheral hard drive that is easily searchable and accessible. If you are a Mac person take a look at the Jaguar presentation. Impressive.
http://www.apple.com/macosx/guidedtour/