eclipse JUNO hangs on start up

I use Eclipse JUNO every day.  However, I couldn't start it today after I restart my Mac.  Mac updated with Microsoft 2011 so I have to reboot Mac machine.  The strange thing happened: Eclipse got stuck.  I manually killed the start up process several times, but it didn't work.  Then I googled it, and found the solution from this post, and here is what I did:

rm $WORKSPACE_DIR/.metadata/.plugins/org.eclipse.e4.workbench/workbench.xmi

Then I can start eclipse, and happy coding.