When Google's Penguin algorithm first went live nearly four years ago, sites that were engaging in black hat link schemes saw massive reductions in search rank and traffic that ended up being very difficult to recover from. At it's best, Penguin helped even the playing field by penalizing sites that were gaming the system through dubious link building. Unfortunately, it also killed some sites whose webmasters were unaware they were doing anything wrong or unethical.
Now, a new and potentially final Penguin update could be on its way. Analyzing your backlink profile can help ensure your rankings don't plummet.