Just pocket money. It's definitely not like I'm making a living off of it.
The real money is in project work of course, but I rarely do those due to lack of time and interest. It has to be a really interesting project then. I'd rather do my own tracks in my own time, how I want and when I want, and then just offer those.
My theory is, that no matter what genre or mood or even filetype you make, someone out there will find it useful for their project at some point. And I think this has been confirmed, looking at requests I've had even for tracks I thought no one would ever be interested in.
Sometimes I get a request for a track only a few days after putting it online. Other times it takes a whole year before someone shows any interest.
But it's always nice to earn some pocket money from one's hobby, and it does add up over the years. To be honest I'm rather hesitant about turning it into a job. I fear I'll lose the interest then. It has to remain a hobby.