I am not part of the big 8... but it certainly does work. Or, at least
used to work. I have only tried it on my own posts, so I am not sure
about thrid party cancels... I see no reason it shouldn't work.

read http://www.faqs.org/faqs/usenet/cancel-faq/part1/
and you need newsservers honoring your cancel messages ...

your best way is ignoring/filtering on your (client) side.

True. And if any poster cannot resist replying to someone who he regards as
a troll, PLEASE identify your response so that others can filter his
responses as well...

Peter