Ya...I can always tell when a hen is getting ready to go broody. She will lay a full clutch (6-10 eggs) with out missing a day then she sits of the nest and won't get off (which always result in a week of no eggs to balance the week of every-day eggs). When they aren't trying to go broody they seem to lay more consistently (2 days on 1 day off).
I haven't let any of them sit on eggs, but talked to someone that had 4 Marans sit on eggs this year. She said that 3 of them made good monthers, but one abandoned the chicks.