If you consider yourself a well-rounded Java programmer you know threads. You must also know or heard about threads in Java 5. Or, the overhaul of threads in this version (and Java 6). This is a complicated topic but whether you like it or not, you must update your skills and learn about concurrent programming in the newest versions of Java.
I just started doing so. I actually feel pretty weak in this area. But I started erasing this gap and I hope to be “up to speed” soon. I ordered Java Concurrency in Practice (supposedly a must have), I ordered Thinking in Java, 4th edition (it is a great book – no, you cannot find the latest version online), and I read about threading online as well, links below.
Like I said, threading is a complicated topic in programming, but if you consider yourself a good programmer, you must master it.
ReferenceConcurrency in JDK 5.0, developerWorks tutorial (need subscription, PDF version)
Introduction to Java threads, developerWorks tutorial
Java Concurrency in Practice, excellent book on threads
Thinking in Java (4th Edition), excellent book on Java with a very good chapter on threads