I joined a few months ago to help plan for our trip in June. I hated forking over the $20, but my thought was that June is going to be brutal hot and busy, so I could use all the help I could get. I think I have got my $20's worth, just from a few things such as best days, best times, ways to tour, where to view parades, secrect trails. etc. My family will never be able to follow a strict touring plan and I wouldn't even ask them to, but we can sure get a good start on our day and get alot done before the crowds kick in. I can report more in a couple of months, but I have enjoyed the info thus far.
I do agree with a previous poster in that the TGM forums are pretty much focused on the TGM way to do things. I, too, am an info seeker and I enjoy a variety of opinions. I love to be able to pick and choose which ideas I think will work best for my family. So use the dis, use tripadvisor, use the unofficial guide and use TGM. They all have good stuff!