PostJoint has reconfirmed their penalty in Google. PostJoint's penalty was for unnatural inbound links, which seems to be Google's stock penalty for blog networks. It was not a new business model violations penalty, as has been reported elsewhere.
There has been lots of discussion that the network actually received a new penalty called a "business model violations” penalty, but this isn't true. PostJoint made a mock-up of a fake Google Webmaster Central warning, however it wasn't really clear to some people that it was a fake warning, especially considering how often people quickly scan articles.
It's now known that PostJoint bloggers have been penalized for participating in this guest blog network. Despite the company's assurances that there were "no footprints" that Google could possibly find and target, some bloggers received a penalty, and have also been inundated with link removal and nofollow requests by those who "bought” links.
PostJoint initially claimed only 16 percent of their network had been hit with a penalty, based upon PageRank only, but they have since removed this statement. However, they confirmed via Twitter when someone asked about how they determined that only 16 percent was hit.
@darrensheffield we looked at sites that lost PR on our system and majority of them are fine.— PostJoint (@PostJoint) April 20, 2014
But since this was removed on the blog post, it's very likely that they've since learned the penalty is significantly higher across the network.
Another user posted a comment that eight of their sites were penalized, yet the ones using guest blog posts that weren't through PostJoint were fine. He also explained that all advertisers can see the URLs within their network, so it would be easy for a disgruntled advertiser to report the entire network, complete with URLs, to Google.
They do have instructions for any of their users who been penalized, including some interesting instructions for their bloggers. They asked that the bloggers notify the marketers via their messaging system when they nofollow any links. But they are asking people to nofollow the links, rather than removing them outright.