http://www.wired.com/gadgets/mac/news/2004/02/62157
The hoaxer, identified only as "Andy," claimed he received a dual-processor G5 for Christmas. But preferring a Windows PC, he swapped out the insides of the $3,000 machine for the guts of a cheapo PC. The post included several digital photographs to prove the outrageous claim.
It generated insults from all over the world, and even threats of violence.
bediger also mentioned the possible presence of "reverse shills" being used to pollute the Linux camp. I believe there may be some truth to that -- it's one way to convince on-the-fence tech execs that Linux/Open Source supporters are extremists.
I also believe there's a parallel in politics: Many political campaigns, when they take the fight into online forums, blogs, and newspaper comment threads, attempt to make the other side seem as offensive and idiotic as possible. Extremist commenters repel moderates who might otherwise be aligned with the cause, and/or attract other extremists. I don't have proof of this (almost all such comments are anonymous) other than the staggering incidence of idiocy I see on comment threads when politicians are discussed.