Interesting article on the Discovery News Website (Why are Speech Recognition and Natural Language Neither of Those?) which says that part of the author's frustration with a telephony speech IVR application was due to his expectations:

[...] The more human the electronic operator sounds, the more I expect from her. When she doesn’t perform, my eye-rolling, jaw-jutting, and nose-exhaling ensues. Japanese roboticist Masahiro Mori (b. 1927) devised a theory around this phenomenon and calls it the “Uncanny Valley."

It says, basically, that humans will tolerate and even show empathy for artificially intelligent life forms (robots, electronic operators) as long as the machines don’t get too big for their britches and start looking and acting all Homo sapiens sapiens. [...]

So what to do? For starters, stop trying to simulate humans, said Bilmes. Keep speech recognition technology on a short leash and use it for applications where expectations are not so high.

He then goes on to give examples where speech recognition makes sense:

• for transcribing voice mails into e-mails (e.g. Vonage);
• for free, voice-activated directory assistance (e.g. GOOG411); or
  
• for command and control and dictation type applications (e.g.  Microsoft Vista’s speech recognition).

Ken