At my university, some programs do check facebook profiles, though I'm not sure how much it influences their decision. They def don't have time to go through every detail and I don't think they'd think it's weird if your profile is private - that's actually considered the smart move.
Btw, if you are a girl (forgot your name) applying to Immunology and Microbiology programs and have a stripper picture on your public facebook profile - you might want to consider taking that down because that did not help your application (though it might help at other schools )