iPhone Application Development

I've been intrigued by the iPhone ever since I bought mine. I have to admit, part of my interest in purchasing a Mac comes from my desire to begin writing applications for the device. I come from a purely web and Windows based application development background, so coding for the iPhone is going to be an interesting change of pace for me.

The biggest issue I've had in the past has been ideas for applications to develop. What would people be interested in, and could I make it worth my while? I've decided since I started this site that there is simply no way to tell without giving it a shot. I've made myself much more open to my own ideas and I believe I'm ready to begin working toward making something new.

Here's an interesting post about an app called Whiteboard Capture. It's an update from the author about how things have progressed 3 months beyond the launch of the application. Notably, the app appears to be generating a very modest but steady return which is simply fascinating to me. Develop a few high quality, useful applications and who knows!

What are some good resources for information regarding app development for the platform? How difficult overall is development for the iPhone for someone familiar with object oriented programming?