Blog commenting used to be a popular way of getting traffic as well as link juice. Then bloggers started getting huge amount of spam comments spending much of their time cleaning them or deleting them. When Google and Yahoo introduced the NOFOLLOW tag for links, it was quickly adopted by many bloggers. Using NOFOLLOW will make sure a link does not get any credit towards its rank.

Commenting for traffic 

Blog Commenting still is very handy in getting traffic. Some blogs get thousands of daily unique visitors. And you can use blog commenting to market your website.

Here are few suggestions you may find helpful:

- Don't spam people's blog. Be nice, make related comments.

- If you have to disagree with any comment, make it professional way, nicely but make your point. 

- Include your website/blog url on the URL Field when you submit a comment. 

- Get a global avatar from a site that offers that e.g. Gravatar.com This will allow you register an avatar for an email address and use it everywhere. If the webmaster choose to show (many does) avatars, your nice little avatar will be there for every comment you make.

-  Find blogs with high traffic in the areas of your interest. You can use the Technorati Popular Blog List http://www.technorati.com/pop/blogs

- Subscribe to the RSS Feeds of the blogs you are interested in. 

- Always use the same name. Many webmaster will show a list of Top Commentators. Using same name will increase your chances to be there.

- This one is very important. Try to be within the first three of the comments. Most people who visit the blog entry read those, and some do click on those links. Make a list of blogs  you are interested in, subscribe to their RSS feeds. RSS feeds generally updated very fast. Whereas with email subscription you will generally get one single email in 24 hours or so. With the RSS feed you can track when a blogger posts a blog entry, and increases your chance to be within top 3.