Siri is built into the iPhone 4S and can speak and understand English (US, UK, AU), French, German, and Japanese with more languages to be added in 2012 including Chinese, Korean, Italian, and Spanish. Here’s more information about Siri.
As an iPhone 4S user I must say I use Siri all the time and while it’s not perfect (it’s still in beta) it really does make things easier.
My wife Anne just got a new iPad and while it does not include Siri, it does have dictation capabilities and it works quite well.
I think Siri and dictation make the use of multi-touch tools like the iPhone and iPad not only easier but fun.