I installed the WWDC 07 release today on my iMac and I really found Leopard to be a relative major upgrade. The speed increase is dramatic, it has to be the 64bit core! Everything opens in less than a second. Rosetta apps run faster too. I installed Office 2004 and it worked very fast. The new Finder is also great, coverflow is a major feature and maybe should be named differently! Preview is also great, just press space and your doc/image pops up. Strangely enough, in this build Preview doesnt support iWork documents! Work and Excel documents work great, powerpoint not yet. The new Desktop is also nice, the new Dock looks great, Stacks are also very useful, especially as an application launcher. The only thing I really dont like is the transparent menu bar. There should be an option to disable it...I have the feeling that the Desktop is still a work in progress and it will be further polished till release. The 3d Dock is great though! The prominent window is really prominent now! The shadow surrounding the window is much bigger than before and makes for a great effect. Time Machine is really easy to configure and is another great feature to have. Spaces I don't like. I use most of my apps in full screen and when pressing F8 to see all spaces ala Expose, I get a preview of all Spaces but I dont get to see all my apps in every Space. I guess it has to do with me using almost everything in full screen. The new Mail and iCal are also looking good, Mail is a good upgrade and I really like the new features (RSS, Tasks, Notes). I didnt get to use iChat because I couldnt make a connection to iChat 3.0 Clients. I guess it is a bug of the current release... My Bluetooth Mighty Mouse didnt work but I guess the final release will solve it also... Overall I have to say that from a user perspective Leopard is a very nice upgrade, without heartbreaking features, but with many major ones. It is also completely rewritten and that shows. The performance is really great!