Ipod app that makes a boatload

I am thinking of buying a mac and buying the iphone app SDK in the summer when i have time to develop an app. The only problem is that i have trouble finding an idea. I have thought of one of two options to find ideas. I can send an announcement out at my school that say something like:

"Do you own an Iphone or Ipod touch? Come down to room xxx and give your opinion to get a shot at a cool $50."

I could also send out a survey on one of the paid survey sites. What do you guys think? Have any other ideas? Also, what's the fastest way to learn iphone development and can you develop it in windows and sell your app in the app store?

If you can program.

You need to get onto building iPhone 3.0 apps!

They will be huge in june when apple releases 3.0

BHOne