Off the top of my head:
Engines under the wing help with the spanwise loading, allowing a lighter wing structure. The engines are also very accessible.
Aft mounted engines mean the wings need to be further back on the fuselage, reducing the moment arm for the empennage (larger tail surfaces needed). Also, more noise in the cabin. And fuel lines from the wings to the engines.
For larger aircraft, the aft engine design becomes less attractive.
BTW, you'll never get a pod strike on a twin with the gear close to the engine.
Last edited by AtoBsafely; 21st Jul 2012 at 16:13.
Reason: Afterthought