“Exposing the Depth JDK 7.0 Applications with DTrace” was the only lab that I attended at JavaOne 08. As you can imagine, it was all about dtrace.
dtrace is a no-overhead, highly dynamic, powerful programming language used to report on running systems. It runs on Solaris, FreeBSD, Mac OS X, and sorely neither Linux nor AIX (the two latter camps will roll their own clones on this one).
The tool itself is really delightful; in the right hands it can really work wonders.
I wish we had this on Windows, Linux, OS/400, and AIX.