Like the other guy said, this is a gray area. A lot of it depends on your relationship with your boss. The main thing is, does this personal work take you over time? If you work 40 hrs/week or whatever and this work takes you over, then you have a legitimate reason not to do it and don't even have to worry about whether it's personal or business.

But if you only have 20 hours worth of work and you refuse to do personal stuff, what are you going to do with the other 20 hours?

More importantly, this is a small business (not like doing your boss's person work on somebody else's dime) how are you going to look your boss in the eye and say no?

When I worked for my boss, I didn't mind doing any personal work for him, as long as it was on my regular hours because he was the company. I mean, who would I complain too? I would even do a little stuff outside of company time if necessary because this was a person who paid me. It's not unlike doing a favor for a friend, neighbor or relative just because you may need a favor back.

But it all comes down to time. If it's beyond your regular work hours, then you would need to get paid for it.