How to use rel=nofollow attribute to discourage SEO spammers

Lately my blog has been flooded with comments on all posts and articles that are very popular. 75% of these comments are lines lie thank you for posting this information, i will definitely follow your instructions and all kind of gibberish. These are comments from all these cheap SEO spammers who want to take advantage of popularity of site or blog to put their links in the comments. After reviewing these comments for some time, I came up with following techniques that you can use to discourage these spammers.

1. This is mother of all tricks. In your content management system (CMS) or blogging engine, make a change to add rel=nofollow attribute to links that are posted in the comments or web site URLs that these spammers have used in their profile. Their main objective is to put a link in your site so that they can get a boost to their ranking. If you add this attribute, that kills their whole motive to put any link in your blog or site. Trust me, this works very well. Google's web spam team invented this attribute purely for this purpose so that other sites can't take unfair advantage of popularity of a site or blog.
2. Do not use a (anchor) tag to display their URLs. Simply put it in a span. Moment they will see that their URL is simply being shown as text, they will not come back to post any comment on your site.
3. Keep record of IP addresses from where these spammers are posting comments. After X number of violations, you can add entry in your web server to block users from that IP address. Or do not allow these users to post comment.
4. Delete the comment if it is too offensive or complete garbage. If they have spent some time to put some few words, you may want to keep it. They are adding some content to your site.

These are very simple techniques you can use to discourage these spammers. In next post I will post some prototype implementation demonstrating how you can achieve this.