This question is specifically related to a recommended architecture and people\'s previous experiences for cross-platform WP7, iOS, Android apps developed
Just adding another alternative to the mix - mvvmcross
This project was developed out of experiences with monocross, mvvmlight, and opennetcf.
It's quite an opinionated mvvm framework (with my opinions in it!), it includes data-binding support for Droid and Touch, and it really does encourage code reuse between the platforms.
The source is available from https://github.com/slodge/MvvmCross, it's been used in at least a couple of large projects already and it's still under active development.
There's an introductory presentation on it on slideshare: http://www.slideshare.net/cirrious/dev-evening-monotouch-monodroid-mvvm-mvvmcross-and-databinding
One of the more fully featured samples is a conference app: