MacBook Air and Airport Connection Timeout problem Solved
I got my MBA (1.8 SSD) on Saturday, and right off I noticed that the Airport didn't seem to be as good as my MacBook Pro. It wouldn't connect in my home office (where the Airport Extreme Access Point is) at all. Other parts of the house were OK but not brilliant. Then on Wednesday I couldn't get it to connect at all. It would see the SSID, but not connect to it (error message was "Connection Timeout"). I tried everything to resolve it: Security Off / WEP / WPA, swapping out the Airport Extreme for my old Netgear 824, restricting the connection to 102.11g only/ b only. None of these worked. But through all the changes my MBP and my work IBM Thinkpad worked flawlessly. Eventually I rolled back the MBA to a timemachine backup from before it stopped working but still no joy. So now I'm thinking hardware fault.
Eventually I rang Apple support, who were really good. The second level engineer got me to create an an hoc network on the MBA which the MBP COULD connect to, but the reverse was not true (the MBA could not connect to an ad hoc network created on the MBP). They concluded hardware fault and I took the Air back to the Apple store and got another machine... which we checked in store, but displayed exactly the same problem when I got home!
So now I'm thinking less hardware fault than interference, so I started turning off any appliance that could interfere (Cinema Display, cellphone, cordless phone etc). But still the MBA would not connect but the MBP always would.
FINALLY I reconfigured the Airport Extreme for 5Ghz 802.11n only, and hey presto - the MBP and the MBA both work flawlessly! Problem solved! (With hindsight I should have tried this earlier). Of course nothing else in the house (Airport Express for AirTunes, Media Centre, work Thinkpad) will talk 802.11n, so I have had to set the old Netgear up to use the Airport Extreme as an internet gateway, and so I now have both 5Ghz 802.11n and 2.4Ghz 802.11g in the house and everything works!
So, in conclusion, even though (the Apple store assure me) the MBA uses the same Airport hardware as the MBP, there is something about its implementation that makes it more susceptible to certain types of interference (although I haven't yet tracked down the source).
If you're experiencing odd Airport failures with your MBA, try different frequencies / channels to check for interference.
MacBook Pro 1." C2D, Macbook Air 1.8 SSD, Mac Pro 2.8, Mac OS X (10.5)