I must admit I was sceptical about streaming HD content with high quality audio (like DD+) versus renting a BD title, but having watched a few now on Vudu at 1080P and DD+ audio, with little or no buffering, it's a very viable alternative to driving out to the video store and finding the title you want to watch is rented out!
I was the same as you, skeptical about streaming coming anywhere close to Blu-ray quality.
But after watching a 1080p DD+ film through Vudu, I was pleasantly surprised by the quality, and the fact that there wasn't any buffering at all. I was actually dumbfounded, to tell you the truth.
Either I had a miracle full speed connection to the US, or the content was being served via an Akamai CDN or similar, because I was getting full line speed (~16Mbps) for pretty much the entire duration of the film.
I couldn't quite believe what I was seeing. (I was checking the real time bandwidth using a tomato router).
I can't remember if this has been answered, but do we know if QuickFlix has local NZ servers, or does it all come from OZ currently?