This is a huge pet peeve of mine. For me, anyway, I click on the name of anyone who comments to see if they might have a blog I would enjoy. And if I like their blog, I follow it. I actually am way less likely to check out someone's blog if they comment "I followed your blog, follow me back!" Especially if they don't say anything else or just comment something generic that makes me wonder if they even read what I wrote. It's not like my not following your blog means I hate you. I'm probably just not interested in the topic. It's not even that I think you're boring, but I am just not interested in tech blogs, for instance, that talk about crazy concepts I can't even begin to understand. And it also makes me a little bit angry that people who comment to follow them back because they followed me somehow feel like they have forced me into a contract to follow their blog just because they have typed 6 words.
So what does everyone else think about asking people to follow you back? Do you do leave comments like that? Do you follow people back just because they borderline order you to?