2 accounts here.
We have 1 that is a joint account. All of my paycheck goes here, and my wife religiously deposits half of her money into this account to help cover our bills and major expenses. My wife kept her own account from before we were married for small purchases such as gas, food, lady products, etc.
I don't have my own checking account, but have a corporate amex and a personal amex that is paid out of our joint account (which also receives my expense checks from work). I pay all the bills through the joint account (which, if you've kept up so far, is contributed to by both of us).
Basically, I want my wife to have a very small fund that she can keep track of. I don't want to have to keep up with her small purchases when I balance the joint account. All large purchases are agreed to by both, if she needs new clothes, she doesn't go blow money without telling me. We've got a good financial trust between each other.
This might sound really complicated, but in practice, it makes perfect sense.
edit: If I didn't have so many work expenses coming in and out of the joint account, we would probably just have one. BUT, it would probably be too hard to keep my wife abreast of what was going on to have just one.