Ars Technica Leopard Review

If you are curious about the changes in Apple's latest operating system there are a lot of places you can look (Apple's list of 300 new features for instance).
The Ars review is different--it goes in to a lot of detail on many of the behind-the-scenes changes and gives you a good feel for where Apple is headed with the Mac OS.
You might want to skip sections that get too technical for you but I highly recommend this review for anyone wanting to know more information than what you will see in marketing materials or television commercial.