I typically do not allow comments on my sites because of the way it messes with your on page seo. Simply put you cannot control keyword density. I excel at on page seo and have everything down to exact percentiles to rank with usually the fewest of links. So its kind of stupid to mess with it. However, I have a blog trying to push a CB product and allowing comments would probably help with conversions due to social proof, etc. Has anyone noticed ranking loss or issues/solutions when allowing comments to posts/pages?