Yeah. I remember the Wolfram Alpha video demo - it looked amazing and natural, but when you got to use the real thing 95% of your queries didn't work at all.

educated guesses:

a) Siri won't work at all, or will degrade to something like Voice Control, if the server is unreachable or you're out of coverage; b) all of your dynamic data (address book, calendar, etc.) needs to be synced to iCloud for Siri to see it; c) third-party extensibility won't be available until iOS 6+.

Extremely skeptical. Perhaps if you speak clearly (sometimes repeating yourself), have a perfect accent and know exactly which phrases it understands.