Oh, yeah, I know. ;-) It's a popular expression. Hillary Clinton, for example, appears to have a lot of "balls", though maybe not quite to match Margaret Thatcher? Condoleeza Rice also.

In my experience, I'd say that when it comes right down to it women are probably tougher on the average than men...once their minds are made up about something. Women who fight their way to the top in politics are usually tough as hell.