Tell It To Me Tuesday: "Put It On The Underhill's Bill"

Ok, here's the situation. (my parents went away on a week's vacation...Seriously, how old will I be before those two statements are not permanently intermingled in my brain?) Let's say you're out to dinner with a group of people. Everyone orders various items from the menu. All order dinners, some order appetizers, others order a few drinks of the alcoholic variety.

Then, the bill comes.

Do you split the bill evenly, or take into account who ordered what? Does it bother you when someone does one or the other?