It seems since my Lion upgrade my MBP has been randomly failing to connect to my wlan. This was fairly annoying and usually had me rebooting a good few times until it seemed to see the wlan network and connect, once connected it was fine, until the next time i booted the MBP or resumed from sleep. It would occasionally see the network in the wifi list, and when I clicked it would return a failure to connect, with 'connection timed out' error. Very useful! My iphone and other devices connect fine, also booting the MBP into windows works fine too, so looks like a Lion problem!
I didn't think too much of it, but today I received my Mac Mini and had exactly the same problem connecting that to the WLAN.
After a bit of digging I found this discussion, and some suggested it was to do with WPA vs WPA2 on 802.11n networks.
So, I swapped my Billion router from WPA/WPA2-PSK to WPA2 and now my MBP connects every time!
Crazy, it seems lion prefers WPA2 rather than WPA, but the shit error message it gives when it decides (randomly i might add) that it won't connect doesn't help diagnose the issue!