There already exists a program that lets you use the iPhone as a microphone for windows. There are a few problems with it. The main problem, which I think would be a problem for anyone who tried to develop such an app, is that there is a large delay from the time that you speak to the time that the sound arrives at the PC. Maybe there is some way to reduce this time, who knows. The other reason that the iPhone sucks as a microphone is that the battery life is too short. Also, I don't think people would really want to use it as their only application, so it would either have to replace all remote functions, or be able to run in the background.
I personally have higher hopes for better more affortable wireless microphone solutions in the future. Amulet will no doubt improve and hopefully they, and others will come out with some good options for us.
If you want I can do a demo with the senstic pocket audio app to show you what the delay is like. Maybe they are just doing something stupid and the delay is unnecessary...
Also consider that if the accelerometer turns the connection off to save battery, there will probably be an additional delay when you lift it before it can connect.