I have a MBA 13" mid 12, OS X 10.7.5. It often completely ignores my Wi-Fi network, not showing it in the list of available networks (my Linux boxes and Android devices are connecting perfectly).
I tried to remove my network from the list of known networks, rebooted my router and notebook many times, tried to change encryption standards (now it uses 802.11b/g, WPA/WPA2, TKIP), but network still was not visible.
My router is TP-Link TL-WR340GD.