In my friend's case, she was at the director level of a large publicly-traded company. Particularly as you approach the top of the that kind of corporate hierarchy, the world becomes very small, and good-old-boy dynamics start to dominate. There's no formal blacklist, of course -- just the opportunity to meet your frenemy from her previous employer down at the bar, where he can confidentially warn you to "watch out for that one: she's a troublemaker". Nothing more needs to be said, and certainly nothing needs to be written.
I suspect that hiring decisions at lower levels will be both more process-driven and better-documented, so it might be more possible to prove the existence of blacklists there (even if it's still far from easy). But near the top of the pyramid, I have great trouble seeing how the punitive legal action can realistically be used to break up the good-old-boy network.
Seeing this play out has actually changed my mind on the necessity of having gender quotas for management and boards. Previously I'd been opposed on vaguely libertarian grounds; now I see it as the only practical way of disrupting the good-old-boy networks that genuinely do a lot of harm. (Society is genuinely damaged -- depriving itself of so much talent -- by systematic bias against women).
Of course, it does happen, in various ways. The way to find out is to find a sympathetic recruiter (or, a "recruiter" who's really your friend), and have them call for a reference for you. There's good fodder for a lawsuit here.
Seemed like a fine solution, but it soon became evident that she had, in fact, been blacklisted: 18 months passed before anybody would even give her an interview, and that was only after deciding to change industries altogether. That silver parachute was, in hindsight, wholly inadequate compensation. Meanwhile her harasser has continued his career with no repercussions whatsoever.
When these problems are cultural / institutional, the threat of a lawsuit will neither benefit the victim nor effect any real change. Takes something more sustained and substantial than that.