Wikipedia has a quite extensive article on the McMansion. I think the author summed things up pretty well without resorting to name calling. The bit about false multipane windows really got my attention since I was noticing that very thing in one of the training rooms at work and thinking who in the world would buy a large window and have a grid pasted on it to try to make it look like a multipane window.
I have to wonder, how long will most of these McMansions will last. It all appears that money is spent more on creating an impression of a grand house instead of creating the actual thing.