Matt Cutt's again shocked the SEO's by Penalising "MyBlogGuest.com". Here have a look at this: http://searchengineland.com/googles-matt-cutts-weve-taken-action-large-guest-blog-network-187028
Yep, it's the only way Google can try and scare people into thinking that buying links will penalize their site. In fact, paid links rank sites and poor Google can't do much about it.
This was expected as so many people started using the site and finally... The backlinks started being considered as SPAMMY! I'm glad I stopped using it a few months ago!