I'm as good as married. I've shared a joint account with my girlfriend for over 3 years. We've been living together just as long, too.
We both maintain our own bank accounts, but have standing orders into a joint account for which bills etc. come out of. We pay different amounts into the account because we earn significantly different amounts (there's a £20k per annum difference between us.) Holidays, Restaurant bills, day trips, house hold applicances etc. are funded by the joint account - providing it's for the both of us! If only one of us is going to get anything out of it, then they pay for it on their own.
We treat each other every now and then to a night out that one of us will pay for, such as the other person's birthday.
We're finding this works well. Impromptu nights out with friends, or impulse purchasing means absolutely no guilt. Not that those sharing a joint account may feel guilty, but we're more comfortable knowing that if I want to spend money frivolously on games/gadgets/etc. then it won't bother her, and likewise what she spends her money on doesn't bother me.
Though I imagine that when we have kids it'll change to a single joint account for everything going in/out and, hopefully, enough to keep a savings account/isa going on the side for the future.