Are you looking at an in-place upgrade of the OS rather than a full reinstall? You might find problems with some licensing. I don't *think* you'll see problems if you're using a network/red HASP key (they were awesomely stable), but it's more likely if you're running a local/green USB lock or an older version of the SPLM.

Same with the AutoCAD license. If it's a legacy stand-alone, keep your Autodesk reseller on standby as there might be extra steps in getting the license re-issued if there's a problem. Probably a good time to review your AutoCAD upgrade procedures, as serious problems might force the issue on you.