I love the oceans. The first map I generated on 1.8 I spawned on an island in the ocean and lucked out with it having a zombie dungeon trees and an abandoned mineshaft below it. And I've been using it ever since. I switch from survival to creative when I'm starting a large build project on it and want to save time. Like my castle on my spawn island.
they don't despawn but they don't spawn either, that's why we have breeding.