It seems google has introduced a new attribute to the href elements the rel=”nofollow”, this attribute tells the bots like googlebot, yahoo slurp, msnbot etc not to follow that link and give the necessary credit to the targeted web page that link points too,
Though this tool is very useful for search engines to combat comment spam in blogs, guestbooks, message boards, referral logs etc it has lot of negative points,
1. Spammers will now be more comfortable in linking to bad neighbourhoods, For example an aggressive affiliate site is always in search for ways to prevent the bots from following the links and detecting the affiliate links, They used to hide it in php scripts, robots file, javascript, css, perl scripts etc, Now they dont need that, they can just say rel=nofollow intheir HREF and bots will just ignore those links, Looks easy isn’t it, now affiliates will be more happy they just dont need to find ways to hide links from the visiting crawlers,
2. Hoard pagerank which has been a long standing debate, before 2 years people used to avoid as less outbound links as possible to prevent something called PR leakage, Even now people are so concerned about pagerank and they dont want to leak pagerank to outbound links, this nofollow tag is a big gift for them, They can just add the tag and search engines will be happy to avoid the link which benefits the site,
In conclude Nofollow is not a great solution to combat comment spam,