Client near the Auckland CBD has working Vodafone DSL but unable to access web sites. DNS on this site is using Vodafone's DNS servers. Change to Google DNS and browsing works. Change back to Voda and it doesn't. Back to Google and it does. Seems conclusive enough for me.
The DNS servers affected seem to be
ns1.ihug.co.nz [203.109.129.67]
ns2.ihug.co.nz [203.109.129.68]
They do ping just fine so they are not completely dead.