I'm quite pleased to announce the availability of Chipmunk bindings for monotouch. I started that last year, and bound just enough of it to get a sample working, added some constraints lately in order to place labels, and completed it since for the beauty of the task. The image next to this is a screenshot from a system using a motor, a gear joint, pivot joints and some more.
Positioning labels on a map, a chart, a plan is a problem every UI developer face at one time or another if he has the chance to work on rich business app. This problem is NP-Hard for non-trivial cases. I faced that issue twice. First while building a silverlight charting library, and then very recently for positioning labels around a pin on a plan. This post isn't about how we solved those two cases. For the charting problem, we went for an algorithmic solution which was working but not optimal. For the second, I don't know how they solved it as I didn't took the job.