I picked up The Undercover Economist at the same time I got Freakonomics, and while I was not that greatly impressed with the latter, I still didn't think The Undercover Economist would actually turn out to be the better book.
My first impression was that it was a wannabe, trying to cash in on the fame of Levitt's bestseller, but I was quickly dispelled of this notion. Tim Hartford does a great job of laying out the fundamentals of demand and supply, with lucid prose and a good storytelling technique. The book is still a very enjoyable read in spite of most of the stuff not being new for someone who devoured Paul Samuelson's classic with a vengeance and topped the single Economics course he took in college (I am talking about *ahem* moi, of course).
One slightly jarring note was Hartford's contempt for Cameroon and its corrupt ways. I'm sure he has travelled to all kinds of third-world hellholes, so he must have had a really bad experience there to stick it to it so much.
Oh, by the way, the Freakonomics Blog's brief stay in my Bloglines feed list is over. Turns out the blog is not even half as interesting as the book.