This thread is pretty interesting. I'm living with my fiancee (we'll be getting married next fall). We just opened a joint checking account to start paying all of the shared bills with. Our plan was to take half our take-home pay and put it into this account. We would pay the mortgage, utilities, cable, etc out of the joint account. Our individual expenses (cell phones, car repairs, our various hobbies) will come out of our individual accounts.
Once we're married, the number of individual expenses will decline, but I think the principle is solid. As the cars and insurance become joint expenses, we can increase the % of our paycheck that goes into the joint account. That way we each always have money that we can spend without a committee meeting.
Neither one of us is going to go crazy with spending, but each of us has spending that would drive the other nuts if we had to look at it every day.
The only challenge I see with this plan is what to do if she stays home with our children at some point.