mluther on "Best plugin for Linkrel (Link Relationships)?"

http://codex.wordpress.org/Search_Engine_Optimization_for_WordPress#Link_Relationships says

There is some debate over whether listing the link relations actually effect search engine ranking however it is simple to implement.

• World Wide Web Consortium (W3C)
• Linkrel Plugin (broken link)
• Link rel Plugin (The plugin is from 2004 and it only does rel prev and next. Our website doesn't break up one article into several pages. So this plugin is not needed.)
• Theme Code (website down)

What plugins are there for linkrel? And which do you recommend?

Bonus question: How important to search engines is listing link relationships?

Thanks.