Guys,
I've been searching for a solution to this problem for months..
I've narrowed it down to Apple's drivers. I booted to linux on my machine and connected to a 5GHz only network just fine. Boot to OSX, and try to connect same network, and get "Connection Timeout".
A different macbook runing Snow Leopard connectes to the 5GHz network just fine.
I got fed up,, so I started playing with the settings on my router. I tried a shorter password, difffernet security settings (WPA2 personal mixed, Aes+tkip, etc...) and nothing worked.
Finally I tried changing the network type from N-only to NA-mixed.
I go to connect, and boom, it connects right away!!!.. grr
TL;DR
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Make sure your 5GHz network is set to NA-mixed if using any OSX Lion and above...