I have a full time job and career but I also have a side business developing desktop and web apps. There is very little overlap between my career and my side business. I have been using my personal website/blog to develop my 'personal brand' around my career. Do I integrate my interest in entrepreneurship, programming and app marketing into my personal blog or should I start a separate website with that information? What about my other social networking sites like LinkedIn?
If the two categories are completely unrelated, separate the two. You can always make up a business name or website and put one of your interests into that category. Obviously, if I'm reading about apps I'm not looking for information on the cars you restore.
If you're just blogging for the sake of blogging, then it won't matter.
I always advise people to start with the home for everything and let the brands grow up and move out as they get to the right size. That way the critical mass of your "home" gives the brands the boost they need. Fans of the home will appreciate the insight while sharing your new brand and fans of just one product will migrate with it.
I've talked about the idea of home, hub and points of contact here: Should company A have different social network identities for each service/website?