I have been having this problem since I use Lion. My Wifi is always full bar, at least that is what it shows. I have great connection speed most of the time. However, occasionally while I am surfing the internet or in the midst of downloading something, it seems that I get disconnected despite full wifi signal. Initially I thought it was my router or my ISP problem, then I check my iPad2 which is using the same wifi network, my iPad2 is able to connect to the internet but my iMac can't. I turn off my iMac wifi and turn it on again and it works well again. Here is the frustrating part, I can't be turning my iMac wifi on/off all the time just to make surf the net, I can't do this too if I am in the midst of downloading something, I have to re-download again and it is a waste of time. Please tell me where went wrong. Thanks.