The second edition covers a lot of the fantastic new features available in Wireshark 1.8+, while not ignoring the functionality of earlier versions. The book covers configuration, capture/display/colorizaton rules (with excellent examples), easy navigation tips, and in-depth analysis and troubleshooting hints for the most common protocols. Lots of free downloads at the book's website - commented trace files (discussed and analyzed in the book), profiles, and videos. Well worth the price!
And don't forget Laura's insightful (and always comical) comments and asides that make her such a superb presenter. They're all here, too. This is no dull, dry technical manual.
I also recommend the test booklet, even if you're not planning for certification. Trying to answer the test questions identifies the most important material in the book, and helps cement the material in memory. Again, well worth a few extra bucks.