i find the zalman flower type coolers the worst, they are fantastic at cooling but they also clog up with dust in weeks.
oddly enough i've not cleaned out my comp for a year, and it's still clean. definitely helps that it's on my desk and not on the floor.
hehe i know i posted this before, but this is what some comps end up looking like inside, hence why i wlays have a few cans of air duster handy