If it's family, they're running Ubuntu, so I use VNC to connect and resolve the issue (hopefully educating them along the way). My wife and I share a machine at home, so I suppose that one doesn't count.

I generally tell friends that I'm not familiar enough with Windows to resolve the issue in a timely manner. I also tell them that I would have to google the problem and they'd be better sending it to a specialist. Afterwards, I refer them to a couple of breakfix shops.

I tell co-workers that it'd be a conflict of interest and I don't do any "computer work" outside of our company.

Anyone else gets a polite "no."