I'm a little worried about point 3. I've done a fair amount of WPF (of which silverlight is a subset) programming on the desktop and while you can achieve pretty smooth animations they still arent as fluid as the ones we're seeing in iOS and built-in WP7 apps. The framework simply lacks some of the necessary support like V-Syncing to make that possible ATM.

That's probably why native apps on WP7 aren't done in Silverlight and I'm not sure how they'll bridge that performance gap.