ehh, well... in my current computer, all ive upgraded are the GPU, PSU and RAM. It came standard with 1 gb of RAM. I upgraded it to 2 gb for the mere price of 130 dollars. I upgraded from the standard 300 watt PSU to a 580 watt one for the price of 60 dollars. And my Radeon X1650 Pro cost me 165 dollars. 3 upgrades. total cost without system: approx 360 dollars. the system itself cost 450. total cost: around 800 bucks. and i am quite certain that this computer could give a more expensive one a run for its money, but that depends on its brand.
this baby was upgraded for sheer gaming performance. and thats what it gives me.
however, i do believe the processor can be better. im not going to OC it, and im not going to buy another one, because it works fine for me most of the time.
and to add some more: i plan on buying an Alienware Aurora mAlx laptop with maxed out specs. i just need to get the money for it. i might also wait for the geForce 9 series cards and get one of those for my desktop.