Well......there's nothing like dofollow exist and you no need to add dofollow attribute.Any page or link is already dofollow if nofollow attribute is not added there. By using captcha and comment moderation option you may avoid spam.
There is NO rel="dofollow" attribute. The rel="nofollow" only prevents the passing of Google PR. Rel="bookmark" specifies a permalink.
Yes this has already been pointed out several times. Anyhow, thanks for the heads up on the no/dofollow issues. I have had the issue clarified now. Thanks guys.