List Compliments of http://www.whydowork.com/blog/blogging-tips/558/

Proper etiquette requires that you don’t spam blogs with useless comments. Simply saying something in the line of “Nice article, I’ll check your blog everyday from now on” brings no added value to the discussion or the community and will most likely be flagged as spam. If you are added to the Akismet blacklist, which is shared by a huge number of Wordpress blogs, you will have a real hard time commenting on any other site. It’s simply not worth the risk.

A proper comment that will pass moderation has to show interest in the actual post and not look like a standard, copy/pasted line. You must read the article and make sure you get the author’s point. If you have no clue what it is about, then you should probably stay out of the conversation. Only once you have read and understand the article should you ask further questions, agree or disagree with the author or share similar experiences.