I've locked up my back wheel a couple of times, once on the sporty and once on the dyna and both times the back end slid forward. Was very hard to control in both cases, avoided coming off in both cases by counter steering but ABS would have made a big difference.
I've locked a few times but easily controlled so didn't think ABS would have mattered, but a couple of times in the wet it would have been super handy. I saw a bloke try to pull up at the lights in the rain a while back and the weight of the bike kept him sliding so it was obviously instinctive to keep the brake on and he slid in front of oncoming traffic. ABS would have helped a heap. I'm for it but one of the blokes at a dealer was complaining about it to me, saying: "You know when you go into a bend too hot and the only way you can get out is to deliberately lock up the back to get the bike sliding so you can accelerate out? ABS wouldn't let you do that." Answer: Um no I'm not familiar with that technigue!