It depends on your intended audience and how perfect you need your video. If you are delivering a standard screencast then a few mistakes during the recording may make it seem more real. If you are looking for professional output I agree with the splitting into chapters and working on a more detailed script (as already mentioned). You can then integrate your into a more comprehensive compositing program like FinalCut, AfterEffects, etc. Overall, I find Camtasia to be the best option available at the moment for screencasting.