I read a recent Philip Hodgetts blog and having installed Mountain Lion on a MacBook Pro decided to try out the dictation function from within FCPX.
And as he points out in his post - it works! (as it will within any application)
http://www.philiphodgetts.com/2012/08/final-cut-pro-x-and-mountain-lion-now...
It makes lot of mistakes but gets the bulk of what you want to say down.
So far I have used it to dictate the words for keyword collections, favourites and titles. In fact anywhere where you would type it will work.
Whether it will actually be a useful function within FCPX, I'm not sure but it's certainly fun to play about with.
As a lot of my work involves mechanical and technical vocabulary and it definitely struggles a bit.
And I just can't get it to swear!
If you say F**k it writes Flock.