Very interesting thread, so here's a kind of summation.
If you're an expert skier with fantastic balance and are always centered on your skis:
Short skis can do everything, however many of you greatly prefer longer skis anyway.
For the rest of us (also applies to expert skiers in many cases)
Shorter skis advantages:
More G forces and energy at lower speeds
Easier to pivot and skid
Shorter skis disadvantages:
Less stable in crud and powder
Easier to get off balance fore and aft
If you are heavy they may flatten too easily and lack rebound
Longer skis advantages:
More stable at speed
Less likely to throw you around in crud and powder
More edge grip once you've engaged the edges
Longer skis disadvantages:
Require more effort to make short turns
Harder to use old style technique (skidding, pivoting)
Harder to bend if you are light.
For me thus on balance a slightly longer ski is preferred. After skiing on 165's for 2 years I like the extra "stuff" of a 175 ski (still not a "long" ski, but longER.)
I will still keep my 165's for teaching and for times that I just want to make a LOT of turns. Also if I lose 10 lbs (which I will, at least, by next year) I may like them more again.
As to the stability, I think that's more a function of the ski. With todays technology, even a short 165 13-m ski is stable at ridiculous speeds. I've had mine about twice as fast as 176 cm bandit would want to go. They do have a tendancy to hunt for turns when running flat, but with a slight edge they will blast just fine. It's a world of difference from the old days.
When it comes to ice, the shorter skis can build a little more pressure and thus have a better grip.