This of course depends on your marketing model. Mine involves promoting an information product on a wordpress blog that is full of helpful articles.
When I started inviting comments, and replying to questions with lots of helpful detail, I found that I almost completely stopped making sales. I assume this would be due to the following reasons:
1. The call to action link at the end of each article is less easily noticed when it is followed by a lengthy scroll of discussion.
2. Many potential customers would see no point in buying a product when they can have their questions answered by the blog author in the comments section
Just thought I'd warn you, you might consider at least testing it yourself. The Thesis theme allows you to switch comments off easily on Wordpress, though I'm sure there are many other ways of doing it.