There are several women at my job who are regularly subjected to what I would call sexual harassment; one of whom has complained to me in the same terms. In none of these cases do the women involved appear prepared to pursue any legal, or even administrative recourse (e.g. physical separation from offending individuals, which could be accomplished routinely), and maintain their working relationships as normal.
I don't want to tolerate sexual harassment or sexism in general in my workplace, so I've spent a lot of time thinking about how to call my coworkers on it without precipitating administrative action that my female colleagues aren't prepared for; but even this means intervening in relationships that aren't strictly mine to address. There's certainly justification in addressing that portion of the behavior which affects me now, but a long-term strategy might be better served by a coordinated approach between mutually concerned colleagues.
Anyone with any insights or advice into these kinds of problems is encouraged to share them below.