I've been working on jQuery full-time now for about 1.5 years (sponsored by my employer, Mozilla). Prior to that I worked on jQuery in my spare time for about 4 years while doing other things (I was in college, then in Y Combinator - Summer 2006, and then worked for Mozilla as a JavaScript Evangelist).
I've managed to pigeon-hole myself into the position of a JavaScript framework maintainer rather solidly (for better or worse).
That being said I really enjoy what I do and have trouble thinking of something that I would rather do as my day job. Being able to work on a piece of code that I've largely written from scratch and promote it to a community of eager users is my dream. I've often thought about making a leap into something else but struggle to think of something that would hold my interest as deeply.
I'm largely not interested in starting or joining a business. For whatever reason I frequently find that attaching a profit motive to work largely impedes my ability to be happy and seems to run contrary to my overall goals (educating people, giving good tools to developers -- and providing both to anyone and everyone, no restriction).
Perhaps I'll find some interesting project some day that will open the financial floodgates (or perhaps I'll enter a situation -- such as having children -- that will necessitate me earning more than I do now) but I'm quite content now where I am, doing what I'm doing.
All this being said, I'm constantly looking at and exploring new things. At the moment though most of that is outside the realm of JavaScript, or even computers, and mostly relating to art. It's unclear to me if that's something that'll hold my long-term interest (although it has for the past few years) but we shall see.