Sites like Wikipedia, Flickr, Google Knol use the rel=nofollow tag for all outbound links thus denying Google Juice to all external websites.

While most big sites use the nofollow tag to prevent spam in the system, Alan Carr is not too happy about this and has created a WordPress plugin that will automatically add rel=nofollow attribute to all links in your blog posts that point to the above sites.

This looks like an interesting tit-for-tat approach but my advice is not to use the rel=nofollow when linking to authority sites because thoughtful outbound links will "show that you’ve done your research and have expertise in the subject manner."

This is true for both humans (reading your blog) as well as search engines. When you use no nofollow, you are directly helping bots discover other useful content on the web and then they too, like your blog readers, will consider you as an expert in that category.