I've recently been testing this theory out by talking to computers as fast as possible to see if they can understand, usually through customer service lines, but some with Siri. The last time was when I activated my credit card and had to read off the numbers. It had no trouble understanding me at a pretty ridiculous speed, something much faster then a person could write down or remember.
In the interest of science: I tested out Siri just now, talking as fast as I can. I asked for: "directions to a violin", "make an appointment for 2:15 am", "what is the temperature". 3 for 3. That thing can handle some pretty fast input!
Interesting data I found surfing around:
Typing speed: 40 wpm Talking speed: 150 wpm Reading speed: 250 wpm (up to 1000 wpm with 50% reading comprehension if you believe speed reading websites)
Clearly pictures are worth a thousand words, so words per minute don't hold a candle to maps, charts and other visualizations. This makes me think reading will still be a big part of interfaces of the future. Perhaps we input with voice and but will have to receive results "on screen." Haha. Ok, maybe Star Trek jokes still aren't mainstream yet. When this is all a reality, will they be funny then? =)