I can't speak first hand as to what it did to American online poker (though "just about killed it" seems accurate), but as far as the rest of the world goes it's meant a huge decline in action and traffic.
Used to be you could log in pretty much any time of the day or night and the major sites (Stars, Tilt) would have loads of games running at pretty much all stakes. STTs were my regular game around the time of Black Friday, and I pretty much never needed to wait more than a minute for one to fill. After Black Friday, I'd be waiting ages, some games wouldn't fill at all. Even now there's often only a few cash game tables running at stakes where before Black Friday there would have been dozens up.
