Some research has been done, and flexibility does impact retention. Flexibility does not positively impact women moving into leadership. I think the message is you might keep them because they're working, they're happy, and they want that flexibility. I know I do; I have children, and that helps a lot, but you still have to make sure there's no stigma along with that in the corporate world. If I take it, then I'm not really giving everything in my job, and then I'm not going to get promoted.
I think women tend to get stuck in middle management for a bunch of different reasons, but potentially that's one of them. It's part of the solution, but it needs to come with a bunch of other things changing.