does anyone here use, or has used, MacSpeech Dictate?

For anyone who doesn't know, MacSpeech Dictate is software that lets you input text by talking into a microphone. I'm currently using it to make this post And it's fairly good.

What do you think of it?
Why do you use it?
Do you have any tips for using the program?
Is there any way to add words?

The only reason I have it, is because it was given to me for free. I'm not really sure if it is going to be much use to me, or if it will make much difference when doing work. My spelling is definitely much better, although I feel silly talking to my computer.