I now know the precise answer - every 8 months. We last went in May, and I have absolutley no idea why, but out of the blue yesterday, my 6yo starts talking of nothing but Disney!! He started by saying he's saving his birthday and Christmas money for Disney, and has been nothing but planning talk since. - And we don't expect to be able to go again for quite a while, so it's news to me! I have no idea why the light flipped on, but I guess that tells me. - If resources were unlimited, we'd go about every 8 months!