I just downloaded a chrome extension yesterday that outlines no follow links on a webpage and DP has no follow links in all sigs, and links in threads and posts. This extension https://chrome.google.com/webstore/detail/dfogidghaigoomjdeacndafapdijmiid How long has this been, I post a link in my sig every time I make a new site thinking it would help SEO.
No follow links still have a value, even if they do not increase PR, Wiki is all no follow, but if you have a link on wiki it drives traffic because it is a trusted site, and therefore your site becomes more trusted.