Arima Yes exactly, I think an option for objects to interact with only those objects in the same layer would simplify things greatly, and also allow us to make more interesting games with the physics. Implementing it shouldn't be too difficult from what I know. I hope Ashley will have time to add this in to his busy schedule :)
Your suggestions 1 and 2 I have thought of, but it feels like too much trouble to go to when the physics engine is just there, and is almost everything you need - especially for making everything more realistic! Suggestion 3 is actually a great idea which I hadn't really thought of. It's a little extra trouble and not quite as neat as I would like it but it could work. The game I'm making is for the mobile though so I would like to not have to use so many extra resources. Let's see if Ashley can find some time to add in the functionality we require :)
aridale Thanks for the suggestion but it'll require a bit too much custom movement than I would like - I also have the problem that the platforms are hills (so slightly rounded!)