Eh you got answers post leh!!!
I too am very keen on what my lecturer has to say about the
question i posted but the bugger aint giving nothing away
Now, for engines mounted below the wings, i would say that they
reduce stress on wings due to flutter/flex etc. It also helps a
great deal in maintenance coz they're closer to the ground(bean
counting). But these engines have very little ground clearance,
check out the 737NGs and are prone to FOD(foreign object
damage)
For rear mounted engines, they're better for landing at terrible
runways, where FOD is a constant issue, as engine is lower to
ground, less likely injest random things on the ground (also means
push-back tractor not req.). They also reduce cabin noise.
However, rear mounted engines mean the Cg is shifted WAY aft,
making aircraft balancing an issue. Also accessing the rear engines
in the case of B727 / MD family, is a serious issue. Another prob.
would be compressor stalls, at high angles of attack, the wing
would be horizontal to the engines, but the air flowing over the
wing is no longer laminar and is now turbulent. turbulent air may
cause a compressor stall, and the most likely time for this will be
on T/O landing
hope this helps 
