Hello,
We’re actually developing our first 2D game with Unity and we’re going through some problems with the physics.
I’ve done some screenshots and a webplayer build to show you anything I can.
Here the actual test scene to show you what’s going on.
What you have to do is to use space for jumping again and again until you see some inconsistencies in the behavior of the two controlled cubes.
http://www.genshoku.net/unity/WebPlayer.html
Here the actual parameters for all things related to physics :
Like we can see on the viewport screenshot, the right cube has a Z collision size of 30 but it’s only 1 for the left cube.
The code used is simply :
rigidbody.velocity = new Vector3 (0f, (float)jumpheight, 0f); for the jump
and :
rigidbody.velocity = new Vector3 (0f, (float)-jumpheight * 2, 0f); for the rammingdown
It seems that there is a difference in physic calculations between a large surface collider and a tiny one.
But our real problem is the tiny bounciness of the left cube across time. I’ve tried many configurations with all the values above and it’s still present. 
Any help on this would be appreciated! Thx