I use the Mac Yosemite (10.10.3) built in dictation extensively, and I find it does a really good job of understanding my speech, at least when I'm speaking in complete sentences.
I also use the dictation commands that you find under accessibility in system preferences, Like scroll down and scroll up. (It even does a really good job of telling the difference between when I say "scroll down" as a command and when I say it as part of a sentence.)
BUT I can't for the life of me get any custom commands to work. For example, I have tried to bind "Close this" to cmd-w, and "tooth paste" to "success" (as an experiment).
I can't get dictation to recognize these commands, ever. I seem to be following the steps shown on every tutorial. It just doesn't seem to work.
(FWIW, I can't get many other commands to work either. For instance, "select previous word" will happily write that text, without dictation realizing that it has just recognized a command! About half the time that I select something and say "delete", it performs a delete, and the other half of the time, it writes the word delete.)
Best Answer
I think I've found the solution to the custom commands. Open your accessibility preferences and press "Dictation Commands". At the bottom "Advanced Commands" must be checked. From there, you can enable all of your user-created commands.