I'm not really sure why, but colleges tend to brag about flooring in thier admissions material, especially in new or renovated dorms that have hard wood floors. I lived in a brand spanking new dorm last year, complete with hard woods, and they were consistently cold and remarkably easy to scratch. This year, I'm in a 1970s era "apartment" with the same cheap carpeting from elementary school. Its ugly and about as easy to keep clean as a toddler.
However, I don't care! I covered most of the ugly carpeting with a fabulous rug:
This groovy little number is canvas, so it will last basically forever and is washer friendly. The colors are a little off in the picture, but its a lovely light blue that looks pretty good with my chocolate brown bedding. Found it at Lowe's, that evil empire of home goods.
So, if you've been assigned to a year of cheap "hard wood" or gross carpet, you'll want a rug that's a) washable, b) durbale fabric, c) not an obscene color. Shag will only trap allergins, and whatever other foul things you might track in, and will probably fall apart if you try to throw it in the industrial strength washer.
If you do put a rug on hard woords, you might want to tape it down to prevent sliding. There are some handy non-skid strips available for purchase, but any tape that won't destroy the finish on wood or rug will work too. Be sure to test an inconspicous corner before duct taping. A good rule to follow no matter what, actually...