Only a subset, which is called /b/. The rest hang out there, and a few related sites, and basically troll themselves. Better to have them (more or less) all in one place than randomly distributed everywhere else, no?

And anyway - not all "trolling" is created equal, IMO. Smart, organised, (dare I say) funny trolling beats random hate and idiocy anyday. I haven't noticed 4chan moving with any particular malicious intent; they just try to amuse themselves, and the causes are as often defensible (Scientology, Sarah Palin mails) as not.

We're always going to have trolls. If 4chan sets the standard for trolling I think we've done pretty well actually. At least they're intelligent.