From Scoble and Israel's upcoming book Naked Conversations, check out their a comprehensive list of Corporate Blogging Tips. Not surprisingly, I think the best tip reflects the "blog as a conversation" model.
Tip #6 Add Comments A good blog is a conversation, not a one-way PR channel. Get over the fact that you won't have control. Instead, embrace the extension. If you don't allow comments your corporate blog is likely to be seen as a PR channel and will be far less likely to be either trusted or followed.
Whether readers choose to use the comments on your blog or not, this is an important feature of blogging in general and corporate blogging in particular. Suffering through the comment spam can be a bit tough sometimes, but if you really want to get the most out of your business blog, allowing people to leave comments (even if they are moderated), is an important step.