I do -- I work with my brother for what used to be the family business. My mother still owns it, but we've taken over all of the work, both doing management jobs but with separate duties.
There really aren't any benefits to working with my brother (rather than somebody else) but I could see how it would be impossible for an outsider to fit in. Since he hasn't worked outside the family business very much, IMO he doesn't act as professionally as he would if he were working for somebody else. I was away from the business for a long time, working for other companies before I took over some of my dad's job when he got sick -- that was a great working relationship, because I acted the same as I would for any other employer.
So, I'm not sure if this problem is just because of my brother's attitude or if it's something that happens when you work for your parents for too long -- I'm thinking of OCC. I know it's on TV, but I can't believe some of the things that the sons get away with on the job, and I can't believe they'd do that anywhere else.
The other thing is we don't socialize outside of work, not that we ever did very much, but we definitely need to put some distance between us once in a while.