I've never tried it on any kind of slick or wet surface though. I'd imaging it would slide out pretty easily, just like any other bike.
As long as you're going pretty straight, you'll still have an uneventful stop even on a wet/slick surface. That's what ABS is for: it detects that the wheel is locking up (based on actual measurements of what the wheels are doing) and releases pressure to avoid a complete lockup. ABS doesn't care about the cause of the lockup (sand on the road, wet road, or just exceeded the available friction on a dry road). My ABS kicks in occasionally when coming to a quick stop on a rough patch of road, where the wheel would have locked up because it was skipping off the bumps and briefly losing contact with the ground (I love Detroit-Metro roads!).
I think it's a good exercise to repeat the ABS tests in a parking lot on a rainy day so you can discover just how much braking power you still have on a wet road.
Of course, just like everything else in the world, there are practical limits to what ABS can do. I doubt it would keep you upright on a solid sheet of ice, for example
ABS also doesn't allow you to slam on the brakes while leaned over in a turn. Even with ABS, the wheels
start to lock up, but do not completely lock up. This means there is still some slippage of the tires against the road surface. Tire slippage while leaned over is not good. The small amount of pulsating slippage while stopping in a straight line is not enough to throw the bike on its side (unless you're on an excessively slick surface, like ice, where the ABS system cannot react quickly enough).
I think it's also important to not think of ABS as a bad thing. When you're stopping and you feel the ABS kick in, don't treat it as a "warning" and let off the brakes to make it stop "yelling" at you. If you do that, you're defeating the purpose of the ABS and you're no longer braking as hard as possible. Just keep braking hard and let ABS do its thing.