Sorry I have several question relative to the same problem.
I am using Netbeans 6.8 on OSX 10.5.8 with java 1.6.0_17 and after about 5 minutes of work, the cpu usage
As you are using Mac OS X, you might try /Applications/Utilities/Activity Monitor.app or /Developer/Applications/Performance Tools/Thread Viewer.app to see what is impacting performance.
/Applications/Utilities/Activity Monitor.app
/Developer/Applications/Performance Tools/Thread Viewer.app