I'm still a duck newbie, but to my knowledge, it depends on the breed. (Good answer, eh? Hah!) We have Muscovies, which are mostly a seasonal layer, but I've read here on BYC there are some who have Muscovies who lay throughout the year (insert jealous aura here). We also have Anconas. We haven't had them for a full year yet, but they supposedly lay everyday, with a few weeks break during the colder season.
I'm sure someone more experienced will pop-in with more information for you, but I was here, so thought I'd get the ball started for you!
chickens dont lay every day either, they take breaks in a weekly laying cycle.
Our Khaki campbells lay better than any chicken could dream of. Our Silver Appleyards are an exceptional layer for a heavy weight breed.
This is my first year with ducks, but this is my experience so far. I have two welsh harlequin females and one buff female. The first one started laying on September 15th and the last one started laying on October 17th. Since October 17th I have gotten three eggs a day every day.
On ocassion my buff tries to lay two eggs a day. This has happened twice that I have found a egg without a shell in there kiddie pool at the end of the day.