I have been wondering on this for such a long time and I couldn't find a definite answer after reading through the forums. Will Google ban people who buy links from the blog network? The one that has a lot in the BST section? (1200 links on 400 blogs, different ip classes $6 -etc) Thanks!
I think the best would be to comment on blogs and articles on similar topics even though it might not increase your pagerank but then it will add to your optimization startegies.
Google won't ban sites which buy links, because everybody can buy a link for their competitor's site.
google not only penalize the sites that sell links, but also coming down hard on paid links. once google identify the links being paid, they will not credit you for those paid links. you will not only not get credit for the links you paid for, but might also get duplicate content penalty. those article blog networks post the same article on the entire blog network which mostly runs on same class C IP. if you want quality posts, then submit to blogs individually and avoid the blog network. some blog network running on multiple class C IP you could probably get away with but i would be very carefull buying from big blog networks
Basically as stated, they do not ban your site they just discount those links that they determined that were paid links. This can happen with any links that you purchase. If you are buying those links for PR, they will most likely not do much good.