Yes, it's true. Commenting on other people's blogs is a good way to get traffic to your website. However, the key is to get traffic, not to post just for the sake of posting...

So what does this mean?

When you post on someone else's blog, you must post something that is relevant and adds value. This is important for 3 reasons:

1) If you make a comment on another persons blog that adds value, chances are more likely that they will keep your comment on their blog and not delete it. If you are unsure, you can contact the blog owner and ask them for specifics and more likely than not, they will appreciate the inquiry and answer your question.

2) It begins to brand yourself as someone who knows their field. The more relevant and useful comments you post, the better you brand yourself. Comments like "yes, this is neat, and look at my site" don't tell the reader anything other than "this guy is spamming this blog." If your comment includes something that adds to a point made in the original blog post, then it looks like you have some experience or knowledge in that particular area, and readers will be more likely to listen to you in the future.

3) People will actually visit your site to find out more about what you have to say. If you leave a comment that adds value, AND leaves the reader wanting to know more, you will get traffic to your site. If it is a blog with a lot of traffic, you will see a steady stream of traffic to your site from that blog. And that is the point.

All in all, in order to get traffic to your website, the only methods that you can rely on that are quick and automated are the methods where you have to pay someone to send traffic to your site. Ways that are free require some thought and effort... The days of automated tools to drive traffic are basically gone. Yes there still may be some ways that work today, but tomorrow, they won't work at all.