Do companies have intellectual property rights to my spare time projects?
answers.onstartups.com
answers.onstartups.com
So I just don't create things in my free time that relate to my day job's core business. And I think that's fair, as they pay me handsomely for all my time and ideas that apply.
Luckily, my hobby interests lie in a different realm than my day jobs usually do, so it shouldn't ever be a problem. Oddly enough, in my interview, they asked me if I was interested in the business. I told them I wasn't really, but I love programming. That turned out to be better for me than I expected. Hehe.