If you run "javaws" (no arguments) it gives the USAGE message. If you add -viewer it launches the cache viewer. Seen w/ 6u3 (on Linux if it makes any difference)

This behavior differed in 1.5.0 where no arguments launched the viewer

The man page says

     -viewer
          Runs the Java Application Cache Viewer (default if no URL is specified).

Meaning if no command line args are given the viewer should launch (according to the man page)

However the technotes disagree:
http://java.sun.com/javase/6/docs/technotes/tools/share/javaws.html
The "(default..)" not is not there.

This was reported by Ubuntu/Canonical.