Duck eggs have larger, richer yolks and thicker whites. As you may already know, many people prefer to use duck eggs for baking because they make everything fluffier. Because they are rich, I have spent a little extra time on the toilet, if you know what I mean... I like to poach mine and put them over braised spinach. Break the yolk and there's your warm salad with warm dressing. Mmmm...
To add to SS's reply...
I have a nickname for ducks. Pigs with Wings. Yep. That's what they are. Mud, drilling holes in the ground, getting muddy trying to swim/preen in 2" of muddy water, splashing muddy water all over everything, watery and projectile poop... But, the eggs... I have a kiddie pool for mine. During the winter I hang a 2.5 gallon bucket for them. Other than the fact that they are so messy with water, no, they are not harder than chickens. Messier, but not harder. Mine stayed outdoors all the time - even in rain, snow, sleet, freezing rain, frigid temps - whatever. They had a 10x10 shed to go in but never did. Not even to lay their eggs. This time will be different for them, though. I am using my 10-12x20' concrete dog kennel for them. No mud... well. Just poop based 'mud'. I'll figure out a way to let the free range after it warms up.