Losing airport connection
I've seen something similar with a WEP encrypted connection.
As a workaround, just turn off your airport card and turn it back on again. That always fixed it for me.
I think the wake up wasn't poperly reinitializing the wep key for the card, so it couldn't connect to the network. kicking the airport card does the re-init.
I've found that adding the key to the keychain has fixed the problem, but if you're like me and have ssid broadcast turned off on your network you won't see the checkbox to add the key to the keychain!
Turn on ssid broadcast, then select your network from the list in the airport menu, and you should see the checkbox to add the key to the keychain. After adding it I have never lost my connection (whereas before, if my system sat idle for as little as 10 minutes I'd have to kick the card).
It drove me crazy for a week trying to figure that one out!