I'm with Bytes Back on this one, I continuously upgrade my system, never have the money to buy all the parts for a new system at a given time.
Currently working on overhauling the rig in my sig right now, little by little, just replaced my cdrw drive, added more memory, have some AS3 on order, and will probably pick up an AX-7 and a 80mm fan to try and straighten out my high temps, then I'll get a new case/psu, round cables, and then on to a new cpu/mobo, possibly new ram if I go ddr (don't see any reason why I won't though).