At a location where there are two print servers, Win 7 was asked to add a printer. XP compatible drivers were loaded on the W2K3 server, but no go. The printer in question was a Toshiba multifunction machine, so drivers are flaky at best.
After going to the support site and downloading Server 03/Vista drivers, everything worked as it should. All that I had heard about XP drivers working out of the box is now just a myth. But it seems that drivers that are/were Vista-ready work just fine.
Keep this in mind during your Win7 rollouts. The thought about printer drivers hit me as I was in the middle of placing this machine on the user's desk...what about printers? Be aware during your testing and make sure that you test any odd printers/faxes/scanner/weird peripherals that you may have, and update the drivers on the spot. So far this is the only thing I have seen that would delay a Win 7 rollout.