I found this initiative, apparently started in Sweden, quite funny but also educative.
So I just set up the Shockingly Big IE6 Warning plugin in this blog.
Then I became curious and checked the stats of this site :
So there is still about 9% of our visitors that are running IE 6 and 3% using some rather outdated versions of Firefox.
And, my god, I would have never imagined that Netscape would appear in the list !
Yes, there is still a lot of work to do about security awareness among users.