How often do publishers sue researchers for copyright infringement for putting their articles on a personal website? I know that some publishers sometimes send copyright infringement emails to researchers putting their articles on a personal website. How often do publishers actually sue researchers for copyright infringement for putting their articles on a personal website? (assuming the authors didn't have the legal right to do so)

I am mostly interested in United States-based authors, but I am curious about other countries as well.
I have never heard of an individual scientist being sued for posting a few articles online (large-scale systematic activity is a different story).  So far, unlike the music and movie industries, scientific publishers appear to have simply not found it worth the cost in resources and community relations to do so (though they've been quite comfortable suing organizations on occasion).

If a scientist decided to resist a takedown order, however, it seems possible that a journal might feel forced to make an example of them.