I, myself, am guilty of spending way more time on Facebook than I should (Twitter is another story - I can't stand it). In fact, I post many times a day on Facebook and have the same, if not more, involved conversations about various topics on my Facebook page. Even the links to my blog posts get far more comments on Facebook than on my actual blog.
As you've probably noticed, my blogging has been rather spotty over the summer. I'm planning on keeping up with my blog posts now that the kids are back in school, but the main reason is because I've been spending a lot of time elsewhere. Facebook.
However, I'd say that blogs are superior for a number of reasons. The most striking one would be searchability and the fact that they last over time. Facebook and Twitter are miserable in that, if you miss it when the posts/tweets go out, you really have to go out of your way to find them. Google doesn't index them either so if you are looking for information on a particular topic, you won't find it there. Also, if your Facebook profile is private, well, then it's as good as not there. And, that's not even getting to the point that you can't really carry out much of an idea in a few sentences or less, let alone in a tweet.
All that said, how do you like to get information? Blogs, Facebook, Twitter, links to blog posts from Facebook/Twitter?