Check out the details here http://blogs.sun.com/nbprofiler/entry/visualvm_1_3_released
I have used this to solve pesky client issues in the past. Recently we had a certain set of client machines looking up during our task processing. Using Visual VM we were able to see exactly where the endless loop was occurring. Sadly for us it was in some third party code but we have been able to concoct a fix and get it out to the client. Just another tool that once you use it you will use it over and over.
Link points you to a download page as the new version is yet to be include with a JDK download and it shows screen shots on how to use it.