As far as I can tell, the current release of the Android SDK (R08) ships without the Swing Desktop jar, and this causes draw9patch to fail.
~$ draw9patch & [2] 52452 ~$ Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: org/jdesktop/swingworker/SwingWorker at com.android.draw9patch.Application$1.run(Application.java:48) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at java.awt.EventQueue.dispatchEvent(EventQueue.java:461) at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176) at java.awt.EventDispatchThread.run(EventDispatchThread.java:110) [2]+ Done draw9patch
The 'fix' is rather simple: just download the JAR for Swing Desktop from here, and drop the swinglabs-0.8.0.jar file into the [sdk-install-dir]/tools/lib folder.
The Swing Desktop project can be found here.
Go check out Patch 15, it's pretty impressive!