We hit a snag with our Macbook. All of a sudden, it wasn't connecting to the wireless network. Upon investigating how "AirPort" - the wireless network client thingy - was behaving, we discovered that, although supposedly using DHCP to get an IP address, it seemed to have assigned itself an IP address which was totally not going to be on the network.
A little searching came up with this discussion - going back several years! And wading through the pages revealed that a) the problem was relatively common, b) had been around for years and c) there was no obvious fix for it.
The links into MacWorld resulted in suggestions like restarting AirPort (which most times made no difference) and restarting the router (which also made little difference - in any case, we knew it was still behaving, as there are all sorts of other things connected to the network and functioning properly).
The most meaningful suggestion I came across was that it was something to do with the Mac firewall. Going to "Security" under System Preferences and then the Firewall tab, I noted that "Set access for specific services and applications" was selected. I added "configd" to the list of specific services, and it started working again. Whether this was the issue, or whether it will continue to work, I don't know. I'll keep you posted.