I'm new to app development, but WP7 is the most poorly documented (probably because it's new), ridiculously locked-down environment to code in I have yet suffered through. Things don't work that should due to intended security constraints, making it impossible to casually develop something in free time that might get made truly useful (read: monetized) later. Frustrating enough that I have decided to compete in the Android app space instead. It may be crowded, but at least I can do it.
"May your future be limited only by your dreams." -- Christa McAuliffe