I think the intro video is too long. For the intro, skip the sign up part, just get right into it. Try to get it under 5 minutes. And invest in a good microphone. It sounds like you're talking into a tin can.
Will order a microphone and see if I can get better quality sound on it, thanks for the shout. I'm normally too busy squirming at the sound of my own voice to notice the quality of the recording!
It would also chop off one minute of an 8 minute long demo.
It's cool that you decided to go with Silverlight despite the fact that it's less tried than Flash. Good luck!