|If you use fleece liners, stains will probably be pretty rare to begin with. Although I have ample sunshine at my disposal here in CO, I don't bother much, as the few stains that happen seem to just work themselves out in the wash over time. I should say, though, that I don't put my diapers in the dryer, which I would imagine would set the stains a bit more.
Once when I was trying to un-stain a friend's diapers before selling them, sunning alone didn't seem to be doing the trick. I doused them liberally with lemon juice and sunned them again, and that worked pretty well.