Here is a great question that was recently submitted:
“Many blogs allow DoFollow links with comments. Can these links ever hurt the Blog’s SEO? And if so, under what circumstances?”
Personally, I think the short answer to this is yes. If you have a trusted blog that is linking out to off-topic and low trusted websites with DoFollow, Google may start to query the external linking strategy and trustworthiness of the blog – thus affecting rankings as trust is one of the major factors, see this previous post.