I've got a couple of clients that has to stay with XP due to their main program they rely on not supporting even Win7 ( Vista never counts ... lol ) and only one so far that doesn't have an option to go to Win8 since their point of sale program version doesn't support it... that company does provide a cloud based system with Win8 support but that is impractical IMO since it relies on an internet connection, something that isn't always available. I have a util I use to create a bootable Windows CD or USB that even has issues on Win7... so I run it in VM like Hyper-V which comes with Win8 Pro.
Overall... My clients that have opted for Win8 are liking it a lot... of course I've set them up how they liked as well which often includes Classic Shell and other tweaks. When setting up a system for a client, we ( the client and myself ) go through their required program list to ensure they aren't going to have an issue with compatibility before they dive in...
When we switched from XP to Win 7 at the college where I work we had a bunch of document cameras that stopped working with the computers. I contacted the company to get a Win 7 USB driver for them and was informed that they aren't going to have any new drivers for them... but I could purchase shiny new document cameras that were Win 7 compatable... at over a grand each... and we had over a hundred of them. I let him know that if his company was going to do that, I would gladly replace every one of them with a competitor's product. Which is exactly what we are doing.

silly narrator was oddly soothing....
How did today's procedure go? 