No Follow Links - Matt Cutts

I try not to take too much notice as to no-follow and do-follow. If your building links, it's good to have a selection of both, it looks more natural - a site that only has links that are do-follow then I imagine Google see's this as unnatural. Of course, I don't know how true this is, but I think it's good to have a selection of both. Obviously, do-follow is probably more beneficial..