By default I think BE.NET adds nofollow to the links posted in the comment body text, but it does not add rel="nofollow" for the URL enter as the commenter's home page.
quick tutorial on how to fix it so rel="nofollow" is added to all links added by users any where on the site:
http://bit.ly/52i4lI
Thanks, good luck!
http://www.sqlblog.ibeckett.com/post/2009/10/Add-nofollow-rel-attribute-by-default-for-comments-in-Blog-Engine-NET.aspxall