As carl said, it depends. I think that if I tried using a voice recorder I'd be more likely to wake up more and forget what I had dreamed. When I write mine down, I'll jot down some key phrases that roughly outline the main events of the dream and then I'll go back and fill in the details. Also, if you don't have much time, jot down at least the main events because that will usually trigger the details in your memory and you can go back later if need be.

-Amé