Well, it really is considered rude to not make eye contact with someone as you are having a conversation. But in informal situations, it happens quite often.
My hubby and I sit back-to-back at our computers and have a conversation without looking up. Or if we're watching TV, we may comment on the program without looking at each other.
The relationship you have with a person (and topic of conversation) makes all the difference whether it's rude or not. In speaking with anyone other than a close friend or relative, I would consider it rude to not make eye contact. Or if you're having a serious conversation with anyone, you should make eye contact.
