I have seen it in work on a final generation Powerbook, and it blows pretty bad at the moment.
For example: Time Machine...
If one partitons a hard drive as follows:
110GB - HFS+ - Macintosh
10GB - HFS+ - TimeMachine
And one configures Time Machine to use the secondary partition on your internal hard disk, upon the first backup and reboot (reboot not necissary to the completion of the backup though), one will remain stuck at the initial OSX Loading screen with the almighty grey pinwheel.
Aside from that, Leopard does run significantly faster when it comes to games (68 FPS in Leopard compared to 54 in Tiger for UT2004).
Aside from that, if you install something, CPU utilization for Installer will easily rise up to 80+% and take about two hours for something like iWork.
Finally, if one were to use Pacifist to install the updated Spotlight over a Tiger installation, you will completely bork Finder. That being the case, it would seem as though the Leopard Finder may be seeing a redesign in the near future to tie in more with Spotlight.
