Apple's demos of the new iPhone 4S' Siri smart assistant are very impressive, but they're just controlled demos. Stuff.tv got their hands on an iPhone 4S and played quite a bit with in a public place. It's still very impressive.
It looks like they were playing with it at the Apple Store in Covent Garden, with quite a bit of noise in the background. Not New York subway level noise, but noisy enough. It worked great all the time. The people tone is pretty natural.