Performance Decay

I'm curious if this plagues anyone else. It seems that if I have my system up for nearly 12 to 24 hours the performance of the machine decays. As in, while at first boot the mouse pointer moves smoothly and precise when the performance starts to 'decay' (best way to describe it) the mouse seems to be less smooth, as in it's jumpy and at times it jumps a lot (if it's in the top left corner of the machine, if I move it just a bit to the bottom it'll jump mid screen and sometimes all the way across). I'm not too sure what could be causing this issue, could it be my Processor, Ram or Video card? Does anyone else have this problem!?

I've got 2gb of ram, a 2.01ghz AMD 64x2 3800+, and a GeForce 6600 GT (PCIe)