My favorite way to learn a platform/language/technique is to just dive in and experiment, so for Windows Phone 7 (WP7) I started writing some apps.
The first one I wrote is “Feedr”, which is an RSS reader:
Here’s the marketplace link (you need Zune installed):
It’s pretty no-frills at the moment, but it does what it says on the box, and is geared towards simplicity and ease of use. What I intend to add:
Feedback is welcomed; I haven’t actually tried this on a real phone (I don’t have one yet). There’s a trial mode available for it.