There is another angle to consider. I'm also a blogger, and I get a lot of comments, and most people are just wonderful and they only like the stuff they see and want to give you their input and encouragement, but ever so often, one comes along that stuffs their comment full of links to another site. Well, I was advised when I was a newbie, not to allow opportunistic people to take advantage of me. One thing is to leave a back-link with an appropriate comment, and another to glaringly try to ride on someone else's hard work. I believe a keyword stuffed comment falls into the same category, it should not be done.