I have always been the type of person that believed that it would be unfair for a search engine to penalize you for having bad links pointing to your pages. The logic is; if I want to outrank my competitor, just make sure to send a ton of bad links to the competitor's Web site and watch it drop down the rankings.
Gary Price over at the Search Engine Watch Blog wrote an entry named Research Papers: Rankings, Link Farms, Personalization, and PageRank Collusion that have downloadable research papers in PDF format, mostly on the topic of Web spam. Many of the papers discuss methods to detect "3rd Generation Web Spam" and then methods to penalize them.
I have started a thread over at Search Engine Watch forums named BadRank & Page Penalization. In that thread, I am hoping to get a discussion started on the possibility, and likelihood of such a penalization to occur. Some papers go to the extent of discussing "BadRank" and a threashold of X before bad links can negativily affect a Web page. It makes you wonder, doesn't it?