I have a blog roll with numerous backlinks to websites with similar content (the same market), they included backlinks to my blog as well. As far as I can tell, they do not have any negative impact to overall rankings. At least I didn't see any yet. Of course, I think they do not have significant (if any) positive impact either. However, if you add a page to your site only for exchanging backlinks and the backlinks are irrelevant then I think it might be considered bad practice by Google in my opinion.