Issues with mesh deformation I have a low poly model that I am trying to rig correctly but even with editing vertex groups and weight painting I am still getting issues when moving around the bones.

Heres the blend file:
http://www.pasteall.org/blend/36971

I undid all my edits to the vertex groups and weight painting so all that has been done is the parenting of the mesh to the armature with automatic weights. Pretty much, Id appreciate if you could figure out whats up with the vertex groups and why they are acting so weird. thanx
Here's a before and after picture to illustrate what I mean. On the left is what happened when I tried rotating the left shoulder using the original vertex groups. On the right is what happened after I reassigned the vertices in the the following groups: abdomen, chest, left shoulder, left upper arm, left lower arm. Double check that you are not only assigning the vertices that you want in each group, but also removing the ones you don't want.