I resolved an issue at a local cafe that was getting complaints from some of its customers unable to use its wifi. When I went observe the problem I had a Apple MacBook Pro and an iPhone with me. And sure enough neither could see the network. I rebooted the macBook into Windows 7 and this could see the network.
The problem was the SSID. The cafe had asked for the SSID to be the name of the cafe which included an accent over one of the characters. Turns out Mac OS, iOS and some other handheld devices were not happy with the accented character. Change the character for an un-accented one and the problem was fixed.
Not suggesting this is definitely the problem you might be having, but is a simple thing to check for whilst you are looking.