I use it a lot. It comes in handy when writing something down or typing it on a laptop is impossible or inconvenient. Some examples:

When I'm driving.
Before sleep / in bed.
When reading a book or screenplay.
While watching a movie.

Especially when watching a movie, I don't want to 'lose the momentum' of watching by stopping the movie and writing something down, so I'll speak into the recorder as soon as something pops into my mind. It could be something like 'Army of Darkness, minute 16, great suspense sequence when zombie jumps out of the water '.

Then I sort out the ideas later.
It's a great tool.

Have tried and failed with the recorder method.

Side note: I have read "The Mezzanine". It was assigned reading for a Critical Thinking course I took in college. I often recommend it to customers at the bookstore -- when we have a copy in stock.

Another side note: I can only assume what type of recording Mr. Baker did of himself for his book "VOX"...

I just remembered a Hollywood Tales post I did here describing the writing process of screenwriter Larry Cohen who relies solely on a tape recorder to work out his stories, then has someone transcribe what he's taped onto the page.