I own the hardcover, and think this is an fantastic RPG product. If you don't have it, Get it!
On a related side note, when clicking the "Powered by GURPS" link on
http://www.sjgames.com/gurps/books/Discworld/, you get to a page saying "GURPS 3rd Ed" on the top, but with a mix of 3e and 4e products. That feels a bit odd, I think the products deserve a revised page.