Not bad at all for the money!
Got a pair of these as part of an incredible package deal of a thermaltake case, psu, 2 x 4gb ddr and have them mounted as rear facing exhaust fans. My main concern, considering their cheapness (my local microcenter sells them for four bucks each) was noise...Happily, this proved groundless. I have them running at 1100rpm and can't hear anything. True, they don't exactly produce a blizzard but with my non-gaming haswell setup, i didn't really need them to.Only downside is that these have 3 pin connectors so i can't control the speed from my 4-pin asus motherboard through its bios, but for my usage it's not relevant enough to warrant deducting even one star.Update 12/13/2014:okay, so now i know why these fans are so cheap...No, mine haven't broken down on me or anything, but i have just installed a noctua 120mm intake fan on my case, and it truly is dead quiet. These kingwins do make a bit of noise but from a sitting position, i would have to strain to notice it. With my ears about two feet away from them however, the noise difference is much more noticeable. Oh well, you get what you pay for sometimes.