@Cry:
However, all clients now have an IP they can't reach as one of their DNS servers…
My mistake, I didn't see him set the WAG200 as a 2nd dns server (the function would not work on the WAG200 in bridged mode anyway).
However, his pfsense box is the primary DNS IP. So I don't quite see it as an issue unless the pfsense box goes down or if he disables the DNS forwarder service for some unknown reason.
In any case, bad choice and the backup dns ip should be removed or changed to say, an opendns server IP.