Since the start of Google Wave there has been a serious issue with the Wave api that has precluded some really cool applications: Issue 406: Robot cannot set a gadget’s state during gadget state update event.

This is a bug that prevents your really cool server side robotic wave participants (robots) from manipulating the state of gadgets (such as maps, forms or any kind of web UI) that are embedded within a wave.

Douglas Linder has provided a patch to to current Java api and a compiled jar file for convenience.  Check out the details here.

But even more exciting is that there is a new api planned for mid February which completely addresses this problem and many more. Details of this can be found on the January 6/7th office hours on the developer wave sandbox  (you will need a sandbox account to view this).