Cogent Communications has joined the club—they're now blocking all of 4chan. I can't even access the site at this point.(EDIT: As of 4:05 AM Central, the entry about Cogent has been deleted from the status blog. No idea why.)
I think Cox Communications may be blocking 4chan as well, as I can't get to it at all. Unless there's a DOS attack on 4chan again, which Encyclopedia Dramatica hints at, so it's possible. (EDIT: It came back up at the same time I noticed moot had deleted the bit about Cogent. Plenty on 4chan are reporting they were unable to get on too, from a bunch of different ISPs. I wonder if this was a technical issue separate from the AT&T issue?)
Are ISPs taking it upon themselves to tell their users that they aren't allowed to go to certain websites? If so, that's not the ISP's job. This is a dangerous precedent if it's an ISP deciding it doesn't want to allow people to go to 4chan due to content.
It's possible that the constant DOS attacks against 4chan (presumed to be by Anontalk) has caused ISPs to cut off access in an effort to reduce bandwidth. Since no one is confirming anything -- this happened on a Sunday, just like every other Internet fiasco (Amazon's homophobic sales rank problem, anyone?) -- it'll be Monday before we know more.
Pic related, as kids these days say.