Dictation is a feature that has become something of a standard for mobile platforms because more efficient text input options are one of the major ex-Nuance talent. Microsoft has voice search in Windows Phone, and has planned expanded voice commands in WP8, but until now we hadn't seen anything about dictation. Those playing around with the Windows Phone 8 emulator saw that there is a new option labeled "talk" in the e-mail app. It's disabled in the emulator, but is expected to be fully working when it hits phones.
The only question here is how extensive the dictation options will be. Other screenshots haven't shown the option in any other text fields, and we haven't seen the QWERTY keyboard for WP8, just the rumored radical slanted keyboard, and even that didn't have a dictation button that we could see. It's possible that this dictation will only be available in the E-mail app, or maybe just E-mail and Messaging. As yet, we don't know.