Yes, sometimes windows will get clogged up with crap that boggs down you're cpu. Think of it like you're body, the fatter you get, the more your heart (cpu) has to work to get blood everywhere. When there is less for the blood to get to, it can focus more power on other things.
Current Build (Hope to finish by late spring):
Intel Q6600 g0
Asus Maximus Formula
geIL Evo 2GB (2x1gb) DDR2
ATI HD3870 X2 or Nvidia 9800 X2?
2x 150gb RaptorX (Have it)
Thermaltake Toughpower 750w PSU (Have it)
Antec P182 Case
HP w2207 22" Monitor (Have it)