Writing excellent blog comments is perhaps the very best way to build your own blog and/or social media presence. Consider a blog comment an audition to show off your own personal awesomeness.
The very best way to be noticed isn't with one really great comment, but rather with consistently good comments in the same place(s) over time. If you become a regular and valued commenter on a blog or site, the other readers of that site will take notice and are more likely to come your way.
Very valid points, in my opinion. As a writer in today's times, being present in the Social Media can help a lot concerning marketing yourself - even for unpublished writers, I believe. As Nathan says, if done well, it can attract the attention of 'important' people in publishing. Which is why I've decided to comment on one blog post of my blog list per day.
Let awareness for me in the blogo- and social-networking-sphere rise to a whole new level!