I installed Leopard on both my Mac Pro desktop and my MacBook Pro laptop. Got most of the problems solved, but printing to my HP4300dtn is a problem - only prints to tray 2, not matter what I do. Even though the print dialog box shows printing to be done on tray 3, it prints to tray 2 regardless. Since we use letterhead and nonletterhead paper, this is a problem that is wasting lots of time.
Also, parallels running Windows XP can no longer print to the HP printer. All was working well under 10.4.
I have tried reinstalling the original HP drivers from the CD that came with the printer - that has not helped.
Seems to be a bug with HP and leopard printer drivers - you can manually set the tray using the cups web interface instead of through the print gui window at http://localhost:631. This will set the default the entire system though, not just for one print job or application. Other than this workaround, i guess we just have to wait for apple/cups/hp to resolve the issue.