Nofollow is a great way to reduce comment spam and keep your site a reputable source for search engines.
Nofollow allows webmasters to tell search engines links to ignore. Nofollow allows either all the links on a page or specific links on a page to be ignored.
It's easiest to show examples of how to use nofollow. If you would like to read more about nofollow, take a look at my references. Examples:
<!-- Hide the whole page --> <meta name="robots" content="nofollow" /> <!-- Hide a single link --> <a href="http://spamPalace.com" rel="nofollow">Keywords</a>
It is important to note that browsers don't use the attribute in anyway. The attribute is only for search engines.
Matt Cutts talks about how no follow stops spammers
Matt Cutts talks about how it appears to some how no follow is taking over the web.