I dropped five grand on my last gaming PC. Water-cooled everything using only the best parts available. It was my college graduation present to myself. Three grand of that was the H2O setup. 100% of the water cooling has been ripped out and sold/given away. Water cooling was louder than air, more complex to fiddle around inside the PC, and although my temps were mildly better, I couldn't reach a better overclock. Current-generation air-cooling really is fantastic. If I could go back in time, I take all the money I spent on water cooling, and put it into another graphics card and the top-tier CPU instead. Which would you rather have - 4.0GHz overclocked and a GTX980, or 4GHz and a pair of GTX980s?
edit: Okay, honestly, I'd take the money and stick it into a couple of stocks that've grown since then. Or if I blew it on PC stuff, I'd get more E3 servers. My tastes have changed a lot!