I actually do exactly as Robin does... except I do some of my brainstorming (actually a lot of it) in Finale as well. While I do enjoy being able to write things down normally (it's so much more satisfying), I do love the benefit of having it played back instantly whenever I please. Unlike Monsieur MuseScience, I like to keep the 'mistakes' and preserve them as much as possible. In fact, on my laptop I have a folder with several files dedicated to copying and pasting away the ideas I don't use immediately for later use. Whenever I need something to fill a section of a piece and have no idea what to do, I turn to these files. I have them for different ensembles and everything! Piano, string quartet, choir, string orchestra, etc. I call them my "Purgatory files" where the ideas await entry into the next life.
My one huge problem when I'm composing is that I come up with an idea and it's fully fleshed out harmonically and everything... but when I try to determine which key it's in I have to plunk around on the piano until I find the right key. At which point I've gotten distracted and no longer am sure if I'm in the key I originally intended and I often forget the harmonic figures I had come up with that were so perfect just 5 minutes ago. This problem arises from the fact that my best ideas come to me in the shower... which isn't the most convenient place to jot things down at a moment's notice. Wet, naked and covered in soap isn't exactly the ideal state to be in if I'm gonna rush to the piano or try and grab some paper and a pencil desperately. So by the time I'm in decent condition to go figure it all out, the ideas have become muddled and are slipping away. It's frustrating as hell. On the bright side though, it gives me a scapegoat for my mediocre compositional achievements. I just blame it on the shower. And the boogie. https://www.youtube.com/watch?v=mkBS4zUjJZo