I was going to say something similiar to what Lisa posted. ANYone can comment about anything, but is that really what blogging is all about? You need a focus, an area, a specific on what you're going to blog about, create a site (niche) and comment on....it's very broad and I personally think that's where a lot of folks get hung up on.
You want to blog, site-create, comment, etc. on something that will make it (niche, topic, area of interest, etc) stand out and make it be remembered and thought about that you want to start an audience and give them a reason to return to you, your blog, site, whatever it is.
And it's not the quanitity of your comment, it's the qualitiy, at least that's what I believe. Sorry for rambling but I couldn't help it-
Renee