Each of us has kept our own accounts and we have yet to open a joint account except for a shared business venture. We split joint expenses down the middle and keep track of who pays what through Mint and a spreadsheet. This allows us to correct when one person has been paying for things more often than the other and it allows us to track spending for things like groceries that would be irregularly split between both of us. Our incomes have been in the same ballpark and our long-term earning potential is similar so a 50-50 split has seemed the fair option. When I want beer and my SO doesn't, I pay, no split. The reverse is true if my SO wants coffee.
Adding to our individual Mint accounts, we have a joint Mint account which has all of our credit cards, retirement savings, and bank accounts added. This enables each person to see the bigger, joint picture for goals like retirement or spending and to have read-only access to the others finances. I really like the joint Mint account because it gives us really good transparency and builds trust while allowing us to maintain independence.
In general we are fortunate to be fairly similar in our financial goals, propensity to save, and spending habits. My SO lives in the now more than I do, but it's an excellent balance to my need to plan and control. In reverse, I'm much better at paperwork and minutia so when I make my roth IRA contribution each year or rebalance my 401k I mention it to my SO. When we were looking to buy a house both names went on the mortgage and the down payment would have been split evenly along with the monthly payments. The paperwork, research, house hunting and so on also all got split down the middle except for when I was out of the country on business. (Yes, I did that twice just after we'd decided to put in an offer on two different houses. To my SO, you're the best ever.)
What's your system for managing money with your significant other? Does it work well for you?