I used Tour Guide Mike, the Unofficial Guide, and the DIS boards for my two trips to WDW (May 2005 and Jan 2006). All three have merit and are very useful.
Just off the top of my head here, there are a few things that stand out about Tour Guide Mike that I did not get anywhere else:
-his "best days" calendar to tell you what park to go on each specific day and
why that is the best park choice and
why another park may be a bad choice. Other sources simply tell you where to go with no explaination as to why. We followed Tour Guide Mike every time and he was always right on.
-I like that Tour Guide Mike has articles relating to specific issues and topics. I just did searches on the things I wanted to learn about and almost always, Tour Guide Mike had written a detailed article about whatever topic I wanted to know about. This also makes printing easier. To be a bit specific there is an article about little hidden places in the Magic Kingdom, quiet places off the beated path to relax that are rarely crowded. My boyfriend and I printed that out and were able to take a rest all by ourselves with the help of this article.
-He had the best parade / fireworks viewing spots of anyone. He tells you where to go for the best view and for the least crowds. Some of this advice I had not seen anywhere else and it all worked like a charm. And he tells you
why certain spots are good or not-so-good.
-I also liked his touring plans for Animal Kingdom better than any other I had read. His plans for AK are different but it makes a lot of sense, so we tried it and it was amazing; worked great. Of course now with Expedition Everest opening, that could all change...
-I liked that he has a set up for your ADRs. You type in what restaurants you want to eat at and on what day you want to eat there and Tour Guide Mike sets the timer for you and even emails you in advance to let you know that it is almost time to make your ADR for the restaurant. I LOVED this feature. I never had to worry about missing my day to make my ADRs. And it was always exciting to get that email.
-He also has THE most DETAILED instructions for getting Cinderella's Royal Table character meal. And yes, I know there are some instructions here on the DIS and in the Unofficial Guide, but I think Tour Guide Mike goes into much more detail about what to expect and what to do every step of the way.
-I also like a feature of his forum that is not here. You can subscribe to be included in a specific month for people who are going during your month so you can talk about issues dealing with that month. For example, I went in May 2005, the kick-off of the 50th anniversary celebration. I was nervous about the crowds and I was able to go in the May 2005 forum on Tour Guide Mike and talk with others who were going in May and what they were planning or thinking about that time. It really made me feel better about the whole thing and it was more intimate to have that.
I am sure there is more, but those are the biggest things that have stood out to me that I am thinking of right now. But I literally used a combination of all three (Unofficial Guide, the DIS, and Tour Guide Mike) to plan my trip and I think that worked out best for me.