I actually like WinXP+SP3. By far my favorite non amiga based OS. Its pretty light (in modern terms), and works nicely.
My main gripe is the artificial restriction to DX9.1.
Would be the ultimate media centre OS otherwise, especially after its stripped back some. I reluctantly upgraded to Tiny Vista for my media centre box when I bought my gf gtx570. Thankfully though I make a point of keeping my mediacentre machine offline.