I used this program for NaNoWriMo last year and it worked very well, but only for certain purposes. I wouldn't find it useful if I were to write an assignment for school, because you have to come up with something to write very fast. But when I used it for writing my novel I just set my goal to five hundred words and thought out the scene I wanted to write in advance. In my experience it works best if you set it to short time or word limits, because for longer scenes you do need to stop and think.
But that said, personally I find this to be something of a gimmicky application, since I have no problem writing concentrated for short periods of time.