This is the first time I've used them to help with a trip, I signed up a few weeks ago and the information on the site alone is worth the cost of membership. The lines app on top of that is a plus! In addition, they've added the touring plans to the lines app now, so you have everything at your fingertips.
In planning our trip, the projected crowd calendar was a key to deciding what to do when. I realize there are no guarantees, but they have a pretty good track record and you can view past days to see how close their predictions were to actual crowds.
JUN 2010 - Caribbean Beach Resort (Star Wars Weekends)
SEP 2011 - Animal Kingdom Lodge
MAY 2012 - Offsite single night and DHS
DEC 2012 - Animal Kingdom Lodge Villas - Jambo House