The best way to describe it is to quote the official description from O'Reilly web site:
This latest title from O'Reilly is a reference to the cool stuff in Swing. It's about the interesting things you learn over the years–creative, original, even weird hacks–the things that make you say, “I didn't know you could even do that with Swing!”
Swing Hacks will show you how to do fun things that will directly enhance your own applications. Some are visual enhancements to make your software look better. Some are functional improvements to make your software do something it couldn't do before. Some are even just plain silly, in print only to prove it could be done. The book will also give you give you a small glimpse of the applications coming in the future. New technology is streaming into the Java community at a blistering rate, and it gives application developers a whole new set of blocks to play with.
Trust me, you want to read it, especially if you like the kind of demos I show on this weblog :)