Back when I was still posting on Bulletin Board systems there was a feature I used to love called "Ignore". You could set your profile up so that any posts by a person that annoyed you simply wouldn't appear. They could thus flame you all they liked and your blood pressure remained low as a result (unless someone quoted them and then you knew).
The feature effectively put the power in the hands of users to ban those they didn't like without telling them. This feature seems to have appeared in an automated type at the lefty San Francisco Chronicle (although they are banning users for everyone). The SFGate website apparently, now has a system that automatically deletes the comments of banned users but still makes the comment viewable to the banned user so they don't know they've been banned.
Note the comment by "JimJams" on the right. This shows up when logged in as that user but when not logged in the comment is deleted.
Evidently there are some people up in arms about this, mostly on the Right because SFGate is on the Left. Personally I think it's a great feature because if you actively ban someone and tell them then they are far more likely to try and get around the ban. By making them think they are still commenting you avoid this (at least for a while anyway).
Of course, there will be those that say this is an affront to freedom of speech. However, the commentators freedom of speech in my view hasn't really been infringed. They are still free to say what they want, they've just been restricted from saying it on someone else's property.
Put it like this. In the real world, if a company banned you from standing in their car park and shouting off your mouth about them, would that be considered an oppression of freedom of speech? Of course it wouldn't, because freedom of speech is about being free to say something, it's not about where you say something.
The banned users are perfectly free to go and start a website up that chronicles all the comments they make that are being deleted after all, or to "expose" SFGate's site administration policies that they dislike as the above link has. Now some might say SFGate's policy is dishonest because it gives someone the impression that they are still involved in a discussion thread when they're not.
I don't buy that line though because if the same user knew they had been deleted they'd still be up in arms about it claiming censorship and all the other expected arguments about how the site is dishonest and doesn't want open discussion. Basically, when it comes to comments you can't win because someone will always scream about being deleted and/or oppressed in some way. The fact that they remain free to moan about it publicly seems to be lost on them.
Update: Just wanted to point out that these sort of things are inevitable now that media organisations are taking comments and thus turning what were static news sites into forums. Anyone that's been part of a forum will know that the "censorship argument" turns up every six months or so. Eventually people will just start linking to previous discussions about it instead of wasting their time writing the same arguments over and over again.