1) System stability. If your video driver dies on XP, hello crash. On Win7 you see your screen go blank for about a 1/4 of a second and then redraws itself, back in business.
2) If you work remotely, RDP is way better. I've even streamed video over RDP and forgot that I was streaming it from a remotely located computer.
3) If using SSDs Win7 will have better perf and longer lifetime.
4) Virtual folders.
But I would say that if your machines are completely locked down, for example all XP machines are not on the internet, just some closed internal network, then I think XP might be doable. Once you touch the internet though, all bets off.