Never underestimate a company's reluctance to change. Usually, the bigger they are (or the more clueless the decision-makers are), the greater the reluctance.
The cost of an upgrade is the daunting part IMO. We need to buy a bazillion CALs (licenses) if we want to switch to Windows 2008 server-side, for example.
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.