Roommates – what are the major areas of conflict? Are there ways to resolve them?

What are the most common issues/controversies that come up between roommates?
Are there any halachic requirements to keep your place clean?
Do you violate Gezel Sheina when your alarm wakes up your roommate?
Can you borrow your roommates’ pots, books, pillow, toothpaste, etc. without permission?
What happens with the kitchen when roommates have different standards of Kashrus?