Wifi Won't Connect; Connection Timeout (Mac)
Been there, done that. I found the source to my problem, but not something that might be a general answer for all with this problem. 

After exhausting the other answers here, I just started trying anything. What I discovered was that I have an external HD connected by firewire, and had it running when I rebooted after installing software. With the drive running, no connection. I shut off the drive and it immediately connected. Go figure! It runs fine of I start the drive after startup, but not during. (Mac Mini C2D 2.54, OS X 10.8.3)

Perhaps the wires acted as antenna or otherwise changed the power available to the Wi-Fi chipset, but I'm not seeing these timeouts after changing my connected devices and cables.