Well most domain names have an abuse email address attached. I emailed a few that belonged to (presumably) compromised hosts sending spam and had no reply and no change in spam volumes. These types of measures are only useful if acted upon.

Similar experience here. Years ago I got emails from Mozilla for a few days in a row about failed login attempts to my account from a certain IP. I did a WHOIS on that and I obtained that it belonged to Fastweb, it was likely some household's dynamic IP. I emailed the listed Fastweb's abuse email address a couple of times, but never got any reply. The login attempts stopped, but I would say probably because whoever was doing it figured out they weren't able to guess my password, not because Fastweb actually did something about it.