If you mean the new speech-to-text for all input fields, all you have to do is press the microphone key on the virtual keyboard (it's just to the left of the space bar). Talk into the phone, and when it translates it you can see if it is correct. Then hit "send" (or whatever you want to do.
I've been using it for text messaging and for Twitter (via Seesmic app) and - for me - it works like a charm.
The Swype keyboard does not support the speech to text feature. The "android keyboard" does. So does the HTC-ime keyboard, much superior (imo) to the android keyboard. Other keyboard alternatives may support the feature, I don't know.