after completing my Direct access course last year on an 04 Honda CBF500 with abs I can honestly say in all the emergency stop and swerve and stop maneuvers I did, I didn't once see the ABS light come on or any hesitation/intervention from the system. we asked the instructor how much force do you have to put through the levers to activate the ABS at around 30-40mph? he said - "I'm not exactly sure about the figures, but it's bloody terrifying when it does kick in, but it has saved a few students from higher speed accidents, but usually they drop the bike anyways, but they do it at lower speeds/stopped. I'll show you what it does when it kicks in if you want!"
he told us to go stand down the bottom of the yard behind some railings and he came down at about 35mph (32 required min for test pass) and pulled hard on the leavers, bloody hell the thing stats to lock the the system releases pressure and applies it again until it locks, then releases, over and over again until a. you release the pressure and control the braking yourself, or b. you stop.
when he took his lid off you could see from the pale complexion, he didn't exactly enjoy it.
personally if I had a big heavy bike like a 1200gs I'd defiantly opt for it, on a smaller bike, I wouldn't go out of my way to have it. Most of the dealers, pro or very experienced bikers I've asked about ABS say if it needs to kick in, 99% of the time it's too late and you were going to have an accident anyway, but abs 'can' slow you faster sometimes.