Comment: XP x64 *IS* Server 2003 (Score 1) 879
Only problem I've seen is that some installers seem to think it's Windows server 2003 not Windows XP.
That's because it IS Server 2003. XP x64 is Server 2003 x64 with Serivce Pack 1, just renamed, and with different features enabled/disabled by default. Check the version numbers: they are both Windows 5.2 (true XP is 5.1). Both XP x64 and Server 2003 x64 also use the exact same SP2 and other hotfixes.
I still use it too, and greatly prefer it to Windows 7. As for the other person that said driver support is terrible for it... that's a common myth. It was terrible in 2005, but now drivers for XP x64 (or Server 2003 x64, since they are interchangeable) are actually pretty common unless you have old/obscure hardware.