Hmmm... I have just re-installed the plugin and it worked fine from:
http://www.avaje.org/eclipseupdate/
I'm using Eclipse 3.4.0
Perhaps try the url: http://www.avaje.org/eclipseupdate/site.xml and make sure that returns an xml document.
Note: Instead of having the old and new plugins at the site only the new plugin is there (so perhaps plugin 'update' does not work but plugin 'new install' does?). Aka perhaps remove the site and then add it back?
The other thing is that the plugin is now under a "ebean 1.1" section which may mean an 'update' is not working?
Hmmm, can you try again and let me know how it goes?
Thanks, Rob.