I go back and forth with the same guy--my boyfriend (soon to be husband?). As much as part of me would love to be dominated by one powerful, anonymous man after another, most of me knows that my happiness lies in a committed relationship.
I think my BF and I are both subs at heart, and we dominate each other as a favor--a little strange! It depends on our moods, as does the switching itself. After a good scene where he's topping me, sometimes he needs to relax into the bottom role at the end. It can be hard for me to come out of sub space, but it's like we have an intuitive knowledge of where we both are and whether we can make the switch. It's rarely uncomfortable. When I'm bottom, I turn myself over completely; when I'm topping, I know that I'm totally in control.
Secretly... my fantasy is for both of us to be dominated by a (non-switch) man or woman--I would love to have by hands tied, being forced to blow him while he's tied down! But there's only the tiniest chance we'd ever do that...