I just encountered several hours worth of work trying to untangle DNS problems in my domain after I demoted a DC/DNS server (illustrated here http://serverfault.com/questions/33463/winxp-using-old-dns-server-ip-even-though-changed-in-dhcp-and-on-the-box ).
There's a stupid group policy (dunno why, but I'll leave it) that was forcing the DNS servers; changed it however the clients can't access the domain (since the primary DNS is down -- why the hell won't windows try the secondary one that is working fine?!?!?)... So how can I force either a group policy override (so that the desktops can find the domain again) or somehow get the group policy back on their computers? Ugh...
I see in there we have the IPs of both DNS servers and then two of our ISP's DNS servers.
The question is -- in an environment where DHCP is handling giving out DNS entries should one override that with DNS from the group policy? Although it burned me here after well-documenting it there shouldn't be a problem in the future -- but I'm left wondering if the policy should stay or go? Are the two IPs of the ISP DNS servers significant (the DNS servers on each DC are set up to forward to those IPs anyway)? Will the clients ever need them?