Tim Bray has an interesting point in The Natural Language Query Fallacy
On computer systems with NLP: "Why would I want to speak to it in full sentences stuffed with subordinate clauses and prepositional phrases? I think I'd want to grunt things like 'Yahoo, Berlin weather' or 'break line 238' or 'spam!'."
Everyone knows of course that spoken language has its own broken grammar, and that's what you need to implement. True interface nirvana is much more akin to a gestural interface - where the computer uses one or more cameras to look at you and detect your state of mind from that (I've often dreamed of a force feedback keyboard so that Windows could drop those pesky 'Are you sure?' popups when I'm angrily beating the keyboard really hard). But that is obviously a harder task.
An interesting related fact is the rise of IDE's and visual tools and the decline of programming languages as the focus of software development attention (as discussed in the classy.dk favourite on Software Pragmatics. When proper computer languages came about in the 60s and 70s that was a revelation. These days, efficient development deemphasizes language, and in fact modern IDE's have something similar to a rudimentary gestural interface. You point and click - tab your way through lists of words to find the right one and occasionally write one or more words by hand.
In short the activity of programming is the complete gestural interaction, not the act of writing.