Comments tags present a wonderful opportunity for most webmasters to help increase the keyword frequency in their HTML code, all the while keeping it hidden from the average visitor. Comment tags provide a way for webmasters to make notes right on their pages. There are comments that can appear in the top, middle, or bottom of a page, and include a wide variety of information. Effective use of comment tags in the HTML code can help in ranking your website for your target keywords. When using keywords in the comment tags, the main mistake that is made is using generic phrases to identify a section and not taking the opportunity to use it for SEO.
Now, whether or not comment tags are really that effective I believe it comes down to how they are used on the page and what search engines factor them into rankings. Most often people take for granted the position that a comment tags holds on the page. Most SEO’s today would tell you that a comment tag in the header is the same as at the bottom of the page. I however do believe there are some distinctions that can be made when using comment tags anywhere on the page. You can decide for yourself on how to best use comment tags for maximum SEO effectiveness on your website. I believe there is no harm in using them for ranking and for usability reasons. If at all, they should help to keep your code organized for quick editing and location, so comment away until you think otherwise.