There was an ok.su that would accept any traffic sent its way: mail, web, im, dns, so on.
I often wonder how many errors sent ok.us traffic to that black hole, and what they did with the data. I assume there are several other .su domains set up with blackholes as well.
As a non-coder, I run some software fuzzing and report the findings to the owners.
With my gear I couldn't spend more than an hour a day setting up tests, but processing the results can take up more time. I've found over 100 bugs in 6 months and it has been fun so far.