How come Android finds lists Wi-Fi networks that OS X doesn't?
1) Possible interferences :

Do you have many Bluetooth peripherals connected to the Mac ?
Try tuning off Bluetooth and connecting to Wi-Fi…
http://support.apple.com/kb/HT1365 

2) Possible mal-functionning hardware :

Check your machine is working with extra channels than 1 to 13 (802.11g) by going in the "Apple" menu, hold down the "alt" key and select "System Information…".

Then in the "System Report…" window select in the sidebar "Wi-Fi" or "Airport" under "Network".

You should see next to :

"Supported PHY Modes" : 802.11 a/b/g/n

"Supported Channels" : 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140

If this is not ok you might need to have your machine serviced as every MacBook Air are compatible with 802.11n. Beware that some channels are banned in some countried thus restricted on your machine : http://en.wikipedia.org/wiki/List_of_WLAN_channels

3) Possible problem with the configuration of the router :

I have encountered sometimes connection drop / timeout with 300 Mbps optimisation (using wide channel configuration 2,4GHz and 5GHz : 20 MHz and 5GHz only : 40 MHz) and some computers. Best would be if the cafes you go to could make sure to have an optimised network for everyone.


If the newtork requires a password : WPA / WPA2 encryption instead of WEP ;
Support for both channels (if using 40MHz with 2,4GHz channels can create performance and reliability issues) ;
For a cafe IP addresses should be cleaned regulary (leased time 1 hour) ;


http://support.apple.com/kb/ht4199