I spent several years as a software engineer developing speech recognition software and noise cancelling technology for extremely noisy environments (think Wall Street trading floors). In order to get consistent and reliable speech recognition performance, a good headset is a must. And if you use speech recognition while traveling (airplane/mass transit), it is essential to have a good noise canceling headset. theBoom noise canceling headset from UmeVoice (http://www.theBoom.com/) allows you to get clear audio into your Mac/PC/cell phone even in very noisy environments. I take my 12" powerbook wherever I go, and the (built-in) speech recognition works great with my Boom. One drawback with theBoom is having to buy an additional USB adapter (from a 3rd party like Griffin) in addition to a "PC" adapter from the manufacturer. However, they say they are working on their own USB adapter.
Review: MacSpeech Dictate