[cfq]

I own and read both books. Mark Pilgrim has a more straightforward approach and his book seems to be more about getting things done. I usually use it to get ideas whilst working on an implementation or use it as a reference.

Whereas Introducing HTML5 is a great read and gives a lot of background information about certain design choices. It also covers almost everything. It's my favourite HTML5 book.

As for one last comparison, I think a newcomer would find it harder to follow Dive Into HTML5 but you get sucked into Introducing HTML5 really fast. In a couple of chapters, it gives you enough to start playing with this new thing you've learnt.