Following the travails of my Vista install at home (and subsequent success), I will be listing my success (and failures) as I gradually re-install my old software and hardware onto this new operating system. As I am running the 64-bit version I frankly expected a harder time than I have got so far, and I have been very impressed. Please note these are my personal findings and should not be taken as an official Microsoft definition of what works and what doesn't: I do not do formal testing on this stuff, I just install things and see if they work as I expect them to. Please also don't ask me about Program X or Hardware Y: I am going to install those things I have and need, and that is it, but in the process hopefully help others who are doing the same or thinking of taking the leap to Vista.
I will update this entry periodically with new information.
Office 2003 Standard: Works
ACDSee 5.0: Works
Nero 7: Works
There are some documented caveats for 64-bit on their site, none of which have effected me.
HP PSC 2210xi All-In-One: Works
Historically I have personally had huge trouble with scanners: I helped several friends and relatives upgrade to XP and everyone that had a scanner that worked on Win9x needed to buy a new one for XP. However, the HP installed a pile of in-box drivers, and the scanner showed up in Control Panel/Scanners and Cameras. Vista doesn't seem to include an actual scanner application, but Office 2003 includes "Microsoft Office Document Scanning" and that works fine. Its a primitive program in some ways (only saves in TIFF format??) but does the job for me, and is a lot nicer than the ugly-as-sin scanner app that came with the XP drivers from HP.
Viewsonic Smart Display: Works
I didn't install the software on the PC, but I just enabled Remote Desktop in Vista and set it to "Allow connections running any version" and it worked. The mouse pointer is often corrupted on the Smart Display, but I haven't seen any other issues. Don't expect Aero on your Smart Display of course!
MusicMatch 10: Fails
As MusicMatch is no longer supported I upgraded to Yahoo Music Jukebox which had the annoying side-effect of setting my Home Page and Search engines to Yahoo, but apart from that seems OK. Yahoo is much better at handling large music collections than the Windows Media Player that comes with Vista for sure.
Windows Media Center: Works (duh)
As this is included with Vista Ultimate of course it works, but if you change a registry setting you can also use it to list and play ripped DVD images. I don't have a TV tuner so haven't tried it as a PVR.