First and foremost, I admit that I love the double-tap approach Apple has implemented in VoiceOver. However, as one becomes more and more familiar with certain apps, it would be quicker to locate a button or link and then activate it via a single tap instead of two. Imagine being able to flick around left or right to find something and then tap once to activate it.
So I suggest that a new setting called "Simple tap to activate" be added to the VoiceOver section of the Accessibility area. It should be disabled by default, but, once enabled, users should tap once rather than twice to activate the control under the focus. Also, it would be great if we could have it as a "Rotor" item -- or it can be one of the items which can be added to or removed from the Rotor -- for easier access. Such a feature would add a good deal of flexibility to VoiceOver.
Finally, it might be interesting to know that the only approach Android 4 currently offers is "single-tap" rather than "double-tap." While that might well intimidate some users who are just being introduced to touch screens, I believe the "single-tap" approach is great for those who know the basics of their screen reader and are now ready to do things faster especially in areas and apps which they've mastered. At any rate, this would excite many VoiceOver users.