Google has always warned that it will deindex any site which gets into buying or selling links or as a matter of fact any link farm activities which can send a wrong impression about a site to Google search engine spiders.
Probably this is a big move where they have come down heavily on Buildmyrank website which was allowing building of the links. Their official spokesman has stated that they are shutting down their activities as majority of their network has been de-indexed (by Google), as of March 19, 2012.
No doubt Google has come down heavily on Buildmyrank which was no 1 leader in the segment of link building activity. No doubt one need to be on the right side of Google as big ginat is watching you and your activities.