Use Siri to dictate to your Mac.

I read a nifty trick earlier today on TÚAW and tried it out. It works! What you do is take an app for your iPhone that functions as a remote keyboard for your Mac, such as Mobile Mouse. With an app on your Mac open and the cursor in a text field, open Mobile Mouse and launch its keyboard. Rather than type, tap the microphone button for dictation, then dictate your text. When done, hit the "Done" button. After the text is parsed and added to Mobile Mouse's text field, MM will then shoot that text over to app open on the Mac.

This does NOT work with the natural language assistant. Just the dictate feature found in the keyboard.