Hi, So I bought a new macbook air 2012 about 2.5 weeks ago. Excellent computer by the way, great to use. Then I upgraded to mountain lion 2 days ago, downloaded in about 25-30 minutes. After ML upgrade, my internet connection speed at home and work has been insanely slow. I have 12Mbps service from Comcast at home. With that, my PC laptop on speedtest is getting about 13 Mbps download and 3.5 Mbps upload at home. Two Ipads in the house are also running internet well, but haven't checked specific speeds. Meanwhile my macbook air is has ranged from 0.2 to 1.2 Mbps download, with upload speed around 3.5 Mbps. At work I don't know the specific network details, but it is subjectively much faster than my home internet, I'm getting 1.5 Mbps download there since the upgrade. I don't have pre upgrade speed tests because the internet was running great before mountain lion. I've been on the phone with apple tech support and to the Genius bar twice. Several changes to network settings have been tried. Along with that, I've reloaded ML from OS x utilities once, and the Genius bar did a clean install of mountain lion once. Nothing has fixed my macbook air from running slow at home. Interestingly (frustratingly) the network speed at the Apple store ranged from about 21 to 35 Mbps download. What the heck is going on? Would the upgrade make my air have trouble interacting with my home internet, but not the wifi at the apple store? I'm going to try and test this on a friend's home wifi tomorrow. If I'm still having problems I think I'm just going to return it. At this point, I would love to go back to lion, but I currently it seems there is no way without having made preparation prior to upgrading to ML, which of course was not done. To summarize, mac is slow at home and work, and fast at apple store since ML. PC at home is fast. Any advice?