Since water is a much denser medium than air, I would imagine that the initial impact would cause either or all of the following: - the plane suddenly veering of its course (comparable to the effect when a car traveling at 65mph hits a puddle) which would position the plane at an angle to the moving direction, thus increasing resistance - the body of the plane suffering structural damage which would further increase resistance - the vertical parts of the plane, esp. engines posing considerable resistance (comparable to the effect of diving flat on your belly into a pool instead of head -first).
I once saw a documentary showing a plane making an emergency landing on water (shot by some tourist who happened to be in the area) - most people inside died, I presume from internal injuries. As I understand, internal injuries (caused by your organs hitting the bones) can be caused by an impact at 35 mph let alone 200 mph.
Anyway, these are the things I ponder each time I fly.
wojtek