Difference between chicken and duck eggs?
I ran across a good resource while looking into duck eggs. I'll let it speak for itself:


  The higher protein in Duck Eggs means
  they mustn't be overcooked, or the
  whites will go tough and rubbery. Some
  people say they will be too tough if
  you completely fry them: they advise
  to rather partially fry them then add
  a few tablespoons of water to the pan,
  cover and let the steam moderate the
  heat and finish cooking them. Most
  people, though, seem to say they don't
  notice a difference between fried
  chicken and Duck Eggs.
  
  Swapping Duck Eggs interchangeably in
  recipes for chicken eggs: some people
  say you can't; others who substitute
  all the time say nonsense, it's fine.
  When the Duck Egg whites are beaten
  they will come up a bit higher owing
  to the protein. They take a minute or
  so longer to start frothing up, but
  then make up for lost time.


There's a great deal more information on the page as well: 
http://www.practicallyedible.com/duck-eggs