Well, the whole dividing evenly thing depends on the situation. No, I don't mind putting in a little more than I really should, 5-10 bucks I guess. But once I went out with a friend for her birthday and we joined a group of her friend's friends. They ordered pitchers of drinks and plates of appetizers - none of us had any of that. They ordered 3 bottles of Port after dinner - none of us had any of that. The bill came, they split it evenly - $70 a person! My total meal w/tip was about $40! I'm sorry, I don't need to pay an additional $30 for crap you ordered without even asking me!
Also, normally I am a great tipper. I have never served myself, but I am in the arts and most of my friends do wait tables. We were at the bar once in college and my drink was $4.50. I gave her a five and actually intended on giving her an extra dollar PLUS the 50 cents change. Well, she gave me my drink and didn't even ask if I wanted the change, just walked off. So I made a stink to my friends. Suddenly, a hand comes over my shoulder and slams the 50 cents on the table! So, I proceeded to rack up a bill and at the end of the night, I left her the 50 cents...and nothing else. Mean, yes. But she was a b*tch...