I hate the 'figure out what you owe' method, simply because it does nothing but generate conflict and acrimony. The people who insist on this method are nearly always the ones who'll claim they didn't eat any of the appetizers or that they only had a single drink and that the service was slow so they're not tipping. Everytime I eat out with these type of people I end up covering for them. Both me and my fiance paid our way through college working jobs where the bulk of our income was from tips, and there's no way I'm shorting a server who does their job just because my companions are asses.

I favour the credit card game, but it's not always realistic, since I'll often be eating out with people for whom a $300 bill is a huge hit to their bank account. I also like the 'I got this one' method, but again, a lot of my friends are cheapskates who never step up, so this one is limited too. This tends to be my default with close friends who I either know will step up in the future or who I don't really care if they ever pay me back or not.

With larger groups containing many people who don't know everyone, I think split evenly is the best way to go. If someone consistently abuses the system just ask them to kick in more. Otherwise who cares? Is $4 a big deal? If you only have $7 to your name what are you doing eating out anyways?