Often, a person will leave a comment on a blog and use terrible spelling and/or grammar. I myself often write way too fast and make mistakes in this area. In this video, Matt Cutts from Google discusses grammar and spelling in blog comments and SEO. He basically says, it is not an issue. However, what he fails to mention is that runaway comment spam, or a long list of spammy comments with links in them, can result in a penalty. While this is the case, as far as small spelling and grammar errors, they should not be an issue for SEO.