This is an iffy topic. Should bloggers enable "Do-follow for SEO," or protect their blogs by using "No-follow for SEO?" Ms. Ileane from BasicBlogTips.com discusses this on YouTube.com.
It's highly recommended that bloggers seeking to improve long-term search engine optimization should enable [no follow for SEO], especially for the purpose of improving commissions from marketing affiliate programs.
Helpful hint: It's a wise idea not to leak your Google pagerank and link juice through a "do-follow SEO outbound linking." Doing a "no-follow SEO link method" will preserve your SEO and Google page rank juice, thus helping your blog ore website steadily improve in Bing.com, Google.com and YaHoO.com.