Google Webmaster Help released a very interesting video that will help you understand a little bit more regarding nofollow links. People wonder if nofollow links would end up hurting the reputation of the website before Google. The true answer for this question is: No, thankfully this type of link will not hurt your site in any way, except you are a spammer. There is no need for you to be worried about the nofollow links since their usage is simply to show the world your site and people can click and open them. Although this is a nice way to build you links some people simply overuse them.
This happens because nofollow links are kept out of the links that Google crawls. Google will only take some sort of action and have your nofollow links hurt your website in case they are used in a spammy way. Google will pretty much just do anything against your rank if it sees your nofollow links all over the web, over blog posts and other pages in a very repetitive way, apart from that nothing should truly make you worry about the nofollow links that you leave online. In case Google finds your nofollow links are not suitable or are being overused they will notify you and will then take further action into the case, which means your page rank will go down and your site will be penalized by such actions.
You can have your nofollow links help you with direct traffic and so on. There is no need for you to worry about them then. Make sure you do not use them in an abusive way all over the web, this would be the only thing that would make Google go after you and your links and reduce your site ranking.
Video: Can nofollow links hurt my site’s ranking?
(YouTube Release: Sep 9, 2013)