The Wit and Wisdom of Discworld is like a clip show for a successful sitcom or the greatest hits cd of your favorite band. It allows you to relive the best bits without all the stuff in between. Each page is like a trip down memory lane. I'd forgotten how funny some of the earlier Discworld books were.
The selections range from witty one-liners to long philosophical paragraphs. While I wouldn't recommend it to Prachett neophytes, it's definitely worth a grab for someone who wants to relive the early Pratchett novels without completely re-reading them.