A friend is blind. The iPhone+voiceover is his primary means of conducting business. We've often talked about UX. Here's what I've learned:

Voiceover is currently an extra layer over a visual interface. So, it amplifies the gesture cost of a visual+touch UI.

After writing a NLP interface for a productivity app, I learned that most of the verbal interaction took less time the visual alternative. It didn't matter if you were sighted or blind. Fitt's law meant that navigating a visual+touch UI was too slow.

So, I'm now working on a verbal+touch UI. In that regard, voiceover users are power users.