Just thought I'd post some feedback on this now that it's been live for some time.  I travel a lot in the Waikato, and recently spent some time in the Deep South.  I'm very happy with the performance and coverage.  I now have my phone (Nokia E71) locked to UMTS and have only had to enable GSM once (Howick in Auckland!) in the last few weeks to make a call.  And data speeds are good also.

So well done Vodafone - I'm one customer who didn't change to XT.