Yahoo NoFollow seems to follow what is going on?

Answer 1

Here is a good description of how all the major search engines handle nofollow http://www.seo-blog.com/rel-nofollow.php

Answer 2

There are two meanings of "nofollow" to search engines.

1. Putting on a page doesn't work for preventing pages from being discovered. Search engines do not re-crawl your site from scratch everytime; they remember previous URLs. What's more, they consider links from sites other than your own. So your very very secret URL could be:
- remembered from a previous crawl, before you put nofollow
- found via a link from a website other than yours.

Meta nofollow was intended for sites which generated dynamic pages such as shopping carts or pages with URL-embedded session-IDs. It says "Crawler, don't lose yourself in this site, it's a bottomless pit of dynamic content."

Meta nofollow is not useful at all for preventing discovery of static or persistent pages. Don't even try to use it for that. If you want to make URLs "secret", then use real security.

2. was invented because spammers were putting links to their spam sites in popular wikis and blogs, vandalizing them. Their purpose was to trick PageRank (and algorithms like it).

rel=nofollow tells PageRank to consider that link unimportant. By putting that on all their user-submitted links, blogs and wikis defeated the purpose of spamming (vandalizing) their sites.

rel=nofollow is ALSO not useful to prevent search engines from discovering new content. Now that blogspam and wikispam has decreased, many rel=nofollow links are valid and interesting, so following them is worthwhile.