I have harvested a list of tumblr URL's with high PR and low outbound links (usually less than 20, mostly nofollow). After tumblr changed the "likes" to 'nofollow' there are still alternative ways to get 'do-follow' links from their blogs. The question is, if there will be an impact to my SERP rankings and Page Rank when I use those links. Google Webmaster Tools show's all tumblr backlinks as coming from one domain. Only in the detailed view you can see the different subdomains. So I'm really not sure about the value of those backlinks. Does any one of you have experience with backlinks from tumblr?