Just thought Id mention my experience with the Windows Experience Index.
Not so long ago I received three brand new carbon copy vostro laptops from Dell. I set all three up on a bench besides each other and performed the initial setup of Vista identically on all three (excluding obvious stuff like computer names etc =D ).
Poking around the computer properties page I decided to run the Windows experience index and see what they got. I thought that it wouldn't be likely that they were all identical but they should be reasonably close. So after they finished doing the test all three laptops showed different numbers to each other. Laptop A showed 3.4, B showed 3.2 and C showed 2.8.
Now call me crazy but that seriously makes me think that the whole Windows Experience Index thing is a complete joke.