I would say it is a hobby if you're not making money from it. And it's not a bad hobby, either. I don't currently make any money from my blog, but if I were to place ads on there or affiliate links, it would be against everything I believe in. I have a couple of writers working with me on a book on some of the ideas presented in my blog and I also make a decent living otherwise, although it is not extraordinary money, but it is enough for me to afford what it is I need.
My website is in the 4,000,000's when it comes to traffic, so I'm sure not going to make millions from it at this point, but I do enjoy it, and the people who read it enjoy it as well. I'm not looking to become some sort of blogging superstar, because I know how much work that would take. And, to be honest, it seems a little upstream to me. Placing big ads on the site would be cumbersome and I hate programming with a passion, and ads for that matter. If I were to try and make money from my blog, I'm sure the money would be negligible, like $20 a month, maybe. And what would be the point of that? 99% of people (or more) will never make a living from blogging, and of that less than 1%, many of them make very little, probably less than I make at a job that is only in the $20,000's a year. So, blogging is mostly a supplemental income at best for most of that 1%. Steve is an exception, mostly because of his knowledge and business knowledge. And very original and timeless content.
That is what most bloggers are missing, and it takes a long time to learn all of it. And it takes a ton of self-discipline and willpower. Things that most people simply do not have enough of. I've kept my blog going for at least 4 years, but there has been times when I didn't post more than twice in a month. And my content is all over the place and I just don't care about the money side of it right now, because I know I'm not there yet. Not only that, I find it rather peculiar that most people go into blogging for the money, and not for creative expression.
I'm no blogging expert, but I do see what it takes to have a successful blog. And I don't think I have all those qualities yet. But for now, I'm perfectly glad having my blog be a hobby and not an income-generating source because it is something I enjoy doing and many people (although admittedly not as many as I want) enjoy reading it. If I could break the 1,000,000 mark in terms of traffic ranking in the future, I would totally start trying to earn money from my blog. But I would do it in ways that felt intuitively right to me, such as books I recommend and other things that support my beliefs and actions.
Anyway, good luck to all you hobbyist bloggers on making a living, but don't put all your eggs in that basket until you actually earn money from it.