Tessellation is the only feature that either DX 10 or DX11, have me excited about.
The other small features are very small in my opinion.
I will be upgrading to DX 11 for the tessellation sometime soon.....probly when the 2nd or 3rd generation gpu's come out, that can handle it much better.
XP has been great for me, and I very much still like it.....I guess for me an operating system is not that big a deal......If i could get tessellation in XP, I would not even upgrade.