I'm sorry if I was a little bit too fast submitting my comment before I really made sure it worked. I'm also just trying to help to solve this problem.
So, here are 3 links where the issue comes up on my computer:
I don't think this will prevent all spam, because it might still work for some people, but lets give it a try.
Work-around 3 worked for me too on a AMD64 Ubuntu 10.04 and this is applied in the Fedora-patch I mentioned in my last comment. So I think the easiest workaround (well, I guess it's actually not a patch) for now is to just port the Fedora nspluginwrapper to Ubuntu until there is a "real" patch.