This has happened to me only twice, but it concerns me nonetheless. Both times, I have decided to post as AC (Anonymous Coward) because of the controversial nature of my comments. Both times, I challenged mainstream opinion with statements by the accepted authorities. Both times, within an hour, my post vanished.
I'm a little torn... I've been participating with the Slashdot community for years, and I'd like to continue because it's "News for Nerds" and I claim that category. On the other hand, I'm 100% against censorship. I'm sure that my participation won't change their policies or practices, and I'm equally sure that they don't make any money from me (I never click ads - ever).
Update: I haven't visited Slashdot in several years. Their slow transition from "News for Nerds" to "Ads, Censorship and Slashvertisements" has caused me to shop for my nerd news elsewhere. Congratulations CNet - you've ruined another one.