I'm at Illinois and we just voted on our new semester's house sweetheart
It's weird to see how traditions like this that are really common and accepted are viewed as illegal at other schools! Gotta love the internet...
A sweetheart is basically just a guy or girl who typically gets along with most of the house. Usually, in our house at least, it's someone's boyfriend, and that someone is usually an upperclassman. A good sweetheart does stuff for the house, like brings candy and gifts or helps out with tasks. He's not required to do anything but it's appreciated! The SigEp sweetheart last year made a jack o'lantern for the guys with their letters carved in it. It's not viewed as a house slut position at all-- it's actually considered a big honor and houses will take out ads in the school paper congratulating the sweetheart on his new status!