Ask HN: demo video do's and don't's

Just about every app homepage these days has a teaser/demo video showing off the goods. I'm about ready to make videos for a couple of my apps, and I'm wondering what are some "best-practices"?

- What software should I use to record the video? - Which video host is best? blip.tv? vimeo? - How long is the ideal video? - Voice narration or graphic pop-ups? - Anything else you can think of?