I think it's pretty common at my school, although I could be wrong. If I remember correctly, certain sororities would "raid" certain fraternities (I think they were chosen and may be different every year). During these "raids" water balloons are thrown, shaving cream and toilet paper is involved, and other items that are generally quite harmless. Composites are taken, but it's almost as though they let us have them. They fight back, but it's all in a fun, loving way.
How do they get their composites back?
They have to serenade the house, usually during Monday meetings.
It really is a good time. There really is nothing to get upset about when you know there is some sort of system to it. People are not out to get other people and/or their belongings.
In fact, click on the link and you'll see a photo of some Sigma Kappas from The University of Arizona preparing to "raid" a fraternity.
http://www.uasigmakappa.com/uask/html/photos.html