I don't know what happened, but this afternoon, my wi-fi connection at home was going crazy. First, the signal just vanished, even though my Powerbook was still at the same location as yesterday - downstairs in the living room. I tried changing channels a few times, fearing that it was conflicting with someone else's network or a cordless phone, or whatever. No dice. Advice I found suggests to try Channels 1, 6 and 11.
In doing so I discovered utilities such as iStumbler and Air Traffic Control for Dashboard, both of which are pretty handy at checking which networks are being detected by Airport and what channel they are using. The only noteworthy difference between the two for me was that the former has a nice looking graph of the samples it takes of the signal, and the latter also displays the type of encryption used. (iStumbler also handles Bluetooth and Bonjour signals)
Knowing what channels were being used didn't really help, since my neighbours were already using different channels. I took the laptop upstairs and put it beside my modem - no dice. The signal was still at zero. Turning Airport off and on, then re-entering my WPA password only resulted in the message "There was an error joining the Airport Network..." I removed any entries for the WPA password in Keychain, typed in the password s-l-o-w-l-y in case of any typos - nah, still no wi-fi.
Finally I shut everything down. Turned off the modem/router, left it off for 30 seconds, turned back on. Then shut down my Powerbook and restarted. Works now.
And you thought the days of "restart the machine if things still don't work" were a thing of the past just because you'd moved to OS X? Think again.
Oh great, my signal just dropped out again - despite my Powerbook sitting here one metre away from my wireless router! WTF is going on here? Restarting the router seems to fix it, but for how long? Aaargh.
I never had these problems when I was using WEP. Maybe I should upgrade my modem, since I'm already on ADSL2+ and it only does ADSL. Then maybe try using WPA2.
I've just found that MAC address filtering doesn't offer much security, since "Wireless clients send their MAC address in the clear, regardless of whether the AP requires WEP or not." I'll test this using a KisMAC, an OS X packet sniffer.