"Very few places" here being slashdot, youtube, reddit, twitter, and pretty much everywhere else on the internet...
You can say anything you want, but you'll probably get modded down and ignored quickly, if not banned.
And even if you don't, you've still got a reputation. Your real identity may not be attached to your posts, but you've still got an identity, and people will at least remember what you say and possibly track down your uses of that identity on other web sites.
Anonymity isn't just a feature on 4chan, it's part of the culture. Nobody can punish you for anything you say, nobody can speak louder than you, and nobody can embarass you because there is nothing linking your identity to your words.
People make a lot of noise about "evil" things being said on 4chan, but that's not quite right. There's a lot of honesty on 4chan. Without any repurcussions, shame, or punishment, everybody can say exactly what they're thinking. They're still thinking it elsewhere -- but they feel like they can vocalize it on 4chan. And there's a lot of interesting, insightful discussion that goes on there, too, especially with regards to subjects that are too taboo or embarassing to discuss in places where you have an identity.