If you don’t know what you are doing with nofollow, noindex and robots.txt you can royally mess* things up (face to face I would use a stronger term). Even if you do know what you are doing, you can still mess things up.
I missed this a few days ago
At the request of WhiteHat SEO community on April the 1st this year all major search engines including Google, Yahoo and MSN Live declared their joint support for a newly developed XFN standard.
The new attribute rel=follow is designed to complement the notorious rel=nofollow. However unlike nofollow attribute rel=follow is designed to express not negative but positive relationship between a linking website and a website rel=follow link points to.
Iâ€™ll try to explain it in laymanâ€™s terms…