Yes, potential employers look at profiles on Facebook. I have a relative who has finally decided to post more about the projects she works on versus what she doesn't like about different types of jobs. I know that if I were an employer and noticed that she thought so many jobs were repetitive, redundant and boring, I would not want to hire her.
So, yes, there are some types of things one would not want to post on Facebook. On the other hand, lets not get paranoid either about everything we put on there.
If a potential employer doesn't like that I support the Constitution, love my cats, love my family and my grandson as well as any of my hobbies, then maybe I don't want to work for them either.
Now, if I were to go there and post things about my coworkers or my patients, then they have reason to be concerned. Posts about my patients could cause me to not get my license or to lose it when I do.
One has to know what to and what not to post.