Java6u21 is released 4 days ago

That's good news  from  performance perspective since it includes the latest VisualVM version (1.2.2)
According to Oracle release notes this include the following functionality

• HeapWalker performance improvements
• VisualVM-Sampler performance improvements
• BTrace4VisualVM plugin introduces BTrace 1.1
• Profiling engine bugfixes
• Built on NetBeans Platform 6.8

It still not a full replacement to a commercial profiler but I hope it will be soon :-)