I'd like to spend more time learning new things, and I get very little of that in my current 40+ hour week job. If I'm lucky, I learn some obscure tidbit at work about once a month. I study on my own time, but progress is slow.
It looks like developing web apps is a good solution, although not the only one. It leverages some of my existing skills. I find the work enjoyable, provided I'm not doing it to excess. And if I'm working for myself, and want to take time off to learn some new skill, I can just do it and not be worried that my manager is breathing down my neck for being "unproductive" for 4 hours.
If I can create multiple small streams of income, I will finally be able to cut down on the amount of time I spend working, and put more time into all the other things I enjoy.
I haven't had any luck yet, but I'm working on it.