Why not just use a framework?
With so many great frameworks out there, why would you need to learn the "raw" or "low level" coding that is discussed in the DHTML Utopia? Technically you would not need to, but if you are like me you have a natural curiosity of what is going on below the covers, even if you use a framework like jQuery. And that understand is what this book gives you. Also no framework will ever cover every use case, so it is good to know the details, in case you need to drop down and "roll your own" solution.
A little dated
The book was published in 2005, which means that much of the material is probably 4 years old (due to the publishing lead times). As a result, the specific browser versions are at least one major version out of date (example: all Internet Explorer discussion are version 6, not the current version). If you disregard the specific discussions, the book does a good job of standing the test of time for 2 reasons: the specific issues that he discusses are still prevalent on the Internet today and more importantly he talks about some great techniques for not coding to specific browser versions anyway.