With the release of Sierra, Mac users can now use Siri and dictation.
Keyboard Commands for Siri & Dictation
|Activate Siri||Hold Command + Space|
|Start and Stop Dictation||Press Function twice|
It should be noted that the dictation commands will only work if your focus is in a text field. Also, if you’re using a trackpad with the trackpad commander, you can use the two finger double tap to start and stop dictation.
Need More Help?
If you need more help on what you can use Siri to do on Mac, check out this article from Apple Support on Siri for macOS.