In a recent video published by Google’s head of search spam, Matt Cutts talks about are blog comments with links spam?
In short, most of the time, commenting and leaving links to your site or resources is not directly spam but like anything, it can be abused.
Matt offers some tips on how to make sure your comments are not considered spam by Google or the site you are leaving it on:
(1) Use your real name when commenting. When you use a company name or anchor text you want to rank for, it makes it look like you are leaving the comment for commercial marketing purposes and thus may look spammy.
(2) If your primary link building strategy is about leaving links in blog post comments and it shows that a majority of your links come from blog comments, then that might raise a red flag.
Here is Matt’s video: