For the extra money you're paying, you're really not getting much. I like the idea of the art book (and almost bought the Wrath collector's edition for that), and the unique pet (which will also give you nerd points in the form of a "feat of strength"). I imagine most people will be buying the collector's edition solely for the pet.
Nice video preview of Cataclysm content in that article; thanks for the link Chaos. I'll not be getting the collector's edition, but when the Cat is finally let out of the bag, you bet that I'll be getting it. Worgies and Goblins look like they'll be quite fun to play, and since my gameplay style in WoW has always been more about exploration rather than endgame content (I've never had a character over 55), this expansion is tailor-made for me.