I have a 2011 Imac 21.5 (the higher end model), I recently just bought this maybe 1.5 months for $1000.00, but this was owned for about 8-9 months from a previous owner. I dont know if this was from the previous owner or happened while i owned it, but 5 small grey lines (2-3inches, hardly visible) appeared on the top left of the screen (Inside the LCD, i took off the glass). It doesn't bother me at all because i only see it in white background, not visible watching movies etc. My use of it is moderate with occasional gaming,SC2/portal, web browsing, and use Servetome (Use Streamtome app on Ipad/macbook air to view all videos/music, kinda like my own Netflix). I've read all 50+ pages of the grey smudges thread, and i don't want that to happen to me so i though I'd share the setup. First i use SMC fan control paired with istatpro to determine what fan setup to use, during normal usage it almost always stays at: Optical 1050RPM Hardrive 2000RPM CPU 2000rpm For torrents harddrive and CPU run around 2500-3000, optical 1000-2000 still experimenting...suggestions? Second i have the arctic breeze usb fans specs: 4 2.0 usb hub at the base fan attached on top adjustable fan speed 800-1800RPM LED knob Bought 2 other usb fans to connect to it Runs relatively quiet compared if i bought a fan small-medium fan. Fan w/o usb dock run at a constant 1700 rpm visit neweeg for more info. Pictures are atteached. That fans sit on twelve souths Back Pack. And no the fans are not directly blowing inside. The third fan pointing down to the desk is cooling of my 1tb blue silicone rugged Ext.HD Before normal use(browsing,youtube, dl torrents(sorry guys i do F) HD-140+ Gaming 140+ CPU-140+ GPU Diode-150+ Gaming 180-190 Gaming for about 60-90min GPU heat sink 150+ Gaming 180-190 all the other stats are about 5+ degree higher than you expect normal to be. After smcfanscontrol and usb fans SMC game settings, ODD 2200, HDD 3200, CPU 2200 HD-105-115 Gaming 110 CPU-99-110+ GPU Diode-118-130 Gaming 135-145 GPU heat sink 115-130 Gaming 135-145 The backside is remarkably cooler under normal days. Gaming is the only time it gets warm, but never scorching hot as people have said. Thats my macbook air sitting in twelve souths BookArc Air also covered in Zaggs invisible shield, I clamshell that a lot and connect it to my LCD 32" to watch movies(using the streaming app) HBOGO and sports on WATCHESPN. After 30-45 min i could hear the fans blowing from a far distance, i stat pro said exhaust fans 3500-4500, ive seen 5000+ on 3+ hours of use, all the temps were well above normal. Plugged in one usb fan to the right where the power would be connected and everything back to normal and the exhaust fans were back at 2000RPM.