I think gestures with combination of buttons has more potential to solve most interfacing challenges than voice. Unless a use-case where the instruction scope is complex enough to want the use of human language, voice as an interface seems more like a fun/cool feature rather than a utilitarian one.

It would be interesting if someone could come up with a list of interface challenges that voice could solve best.

One that I would like to have is a writing platform/software that is entirely functional with voice. Something of a similar nature: http://harrypotter.wikia.com/wiki/Quick-Quotes_Quill