I am thinking about the ability and timing of our users to move to Leopard. Here are some specific items to think about:
No more Printer Setup Utility. Use the new Preferences panel instead. Windows printing seems to have become more challenging, but we have improved our ability to script the addition of Windows printers.
Printing duplex and landscape don’t appear to work with Samba printers.
It has become a lot harder to find a network volume after you have connected to it — no more desktop icon, and now OS X connects all the way to the share instead of mounting the network share.
The default download location is now Home -> Downloads. This will throw a few people, though you can change it.