The reason behind the change is a simple one. They do not (currently) fudge NXDOMAIN records like openDNS do. This has a tendency to break RBL queries, openDNS "solves" this problem by making exceptions for known RBLs. As you can see from this OLD discussion on the openDNS forums
this has been their policy for a long time.
The default RBL services used by the movable type spamlookup plugin are bsb.spamlookup.net and sc.surbl.org. I also use additional lookups like stopforumspam
and others. As a result I was constantly experiencing false positives for comments and trackbacks. Changing to google solved all these problems. If you are using niche RBLs and openDNS I would recommend that you test these.
$ host nopes.grrrr.bsb.spamlookup.net 184.108.40.206
nopes.grrrr.bsb.spamlookup.net A 220.127.116.11
!!! nopes.grrrr.bsb.spamlookup.net A record has zero ttl
$ host nopes.grrrr.bsb.empty.us 18.104.22.168
nopes.grrrr.bsb.empty.us A 22.214.171.124
!!! nopes.grrrr.bsb.empty.us A record has zero ttl
$ host nopes.grrrr.bsb.spamlookup.net 126.96.36.199
nopes.grrrr.bsb.spamlookup.net does not exist at google-public-dns-a.google.com, try again
$ host nopes.grrrr.bsb.empty.us 188.8.131.52
nopes.grrrr.bsb.empty.us does not exist at google-public-dns-a.google.com, try again
I have taken the liberty of reporting these two to openDNS as they are common for MT users, however there are several other RBLs that I use which aren't covered by openDNS. By changing to google public DNS I don't have to put up with false positives. It also saves me the hassle of having to verify and "fix" RBLs every time I make changes.
If you want to make the change you can find the details at: http://code.google.com/speed/public-dns/