Hi, my comments below:

: I was reading "How a paddle works" on Nick's website last night. He
: states that "As a general principle it is more efficient to generate
: a propulsive force by pushing a large mass slowly than it is to push a
: small mass quickly." This is exactly what I feel when I paddle with a
: large Euro blade as opposed to a GP.

I've been thinking about that too. In boating, the propeller's efficiency is limited by the slip. If a prop slips a lot - ie. moves small amout of water but faster - the efficiency will be lower.

I'm not sure if that works same way with blades, but it can be. However those who can use both blades well usually do not say that GP would be less efficient than euro.

: Joy mentioned that she had trouble rolling with a Euro paddle because of the
: feather angle. Keep in mind that if you like Euro paddles, rolling is just
: as easy if you keep it unfeathered. In fact, I always suggest an
: unfeathered paddle.

For joints the unfeathered paddle will be good, but I don't think it will be good in paddling. The upper blade will have lot's of wind resistance if the blade is not feathered. Using the feathered paddle need the correct technology.

My GP pro's and cons are (plus the stuff that has been said before):
+Volume in blades and no feather means it's a great outrigger. If you stop paddling, just keep the paddle extended and practically you can not capsize the kayak.
+Longer tips means that there's less change to miss the stroke in waves. Usually people with Euro paddles capsize when they swing paddle which is not immersed properly.
+Nonfeathered blade is calm at winds. I felt that wind gusts tend to pull the feathered wing paddle in a bit awkward ways.
+GP is always in right way and right angle. No need to think about that if you capsize. It's more fun to play with rolling and such too.

-Efficient use of GP is more difficult. It will require the canted blade technique which is not easy.
-Hands will travel close to the water surface and thus the hands tends to get wet.
-It can be difficult or to use the GP properly in wide and high non-greenland kayak.

This was the first summer with GP for me, I had been paddling with feathered wing paddle for couple years before that. I'm still quite poor with the stick, the beginner style will go easily, but canted blade not.
My first GP was done by the makegreen2.pdf (or something). However I feel the paddle came out really too big (230cm x 9cm). I'm now using much better paddle, it's 220cm long and around 7,5cm wide. The difference is major especially against the wind. I'm still not sure if I should have the version with shoulders or not.

Btw. Today was the pool day - I tested upside-down paddling and it went pretty well, I did over 10 metres in my second attempt. One guy was trying to do it euro paddle and it looked so much more difficult. It's fun to play in pool, especially with GP!