How bad are rusty drum brakes?

I have a 2001 Ford Focus with rusty rear drum brakes. I haven’t had any braking issues as of now, but every time I walk around my car I get a little squeamish - they are VERY rusty. Should this be checked out?

I assume that you are referring to the exterior of the rear brake drums.
If so, that does tend to be the norm after a few years.

What really counts is the condition of the wheel cylinders, the inside of the drum, the brake shoes, and all related hardware. Rather than waiting for “braking issues”, I would suggest that you have the rear drums pulled the next time that the car is in the shop for an oil change. With any luck, only the exterior of the brake drum is rusted, but it pays to have things checked out proactively.

It is normal for them to rust. In almost 50 years of driving, I have never had to replace a brake drum. If it makes you feel safer, having it checked by a trusted mechanic would be worth the cost. While you are there have him take a look at the brakes in general.