My Wife and I have done a few just to get the freebies, the time share places hate us since we are really good at the good/bad cop routine. Never once left signing anything, and a few times got the follow up calls with the continual badgering to do sign up. A couple of time they were even willing to cut a better deal over the phone after you walk away.
Most are not worth it that is for sure, unless you travel all the time and willing to go places when they are not busy. It just does not fit most peoples schedules and lives.