Overall they are awesome. Our new house has one and we turned it on the other night and it really cooled the house down especially since we opened several windows. A few minutes of that and there was no reason to turn on the AC. It was just lovely.
BUT important. If you turn on your attic fan, be sure to close the flu on your fireplace. The draft was so strong that it pulled air down the chimney which pulled out ashes all over the house! That tells you how crazy our weather has been - one week we are building a fire and the next possibly needing AC!
Pictures of some progress (with all the ashes mopped up!) coming soon!