I think it is worth the money, especially if you can get a discount. On the other hand, I think the Unoffocial Guide is much more valuable and much more bang for your buck. Whenever TGM's itinerary advice differs from UG's I go with UG. I'm not sure why, because I know TGM makes a good living at giving tours.
I find the TGM site very hard to navigate. In some ways, it has both the worst features of the print material (outdated by DIS standards) and the worst features of web material (takes forever to sift through it, and find what you need). I also find annoying the condescending asides and comments ("And we DON'T want to be late for Wishes, DO WE Mainebound???..."). I'm quite sure the author would not have such a successful tour business if he spoke to his clients in real life like that!!
But I don't regret purchasing it. It was only $15 bucks, and there's a lot of material there, including lots of pics, for beginners and pros alike.