ABS is a worthwhile addition when finding yourself in "fight or flight" split-second decision making scenarios. I've personally witnessed a distracted sportbike rider (~05 gsxr 750) endo himslef and the bike when slamming on the front due to lack of attention & keeping proper distance between himself and the killer cars porschenut mentioned.
Riding any motorcycle takes a huge amount of wherewithal and constant scanning for threats. Everytime I hop on my bike, I mentally prepare myself for the journey. In a way, its a job -- and why I enjoy it so much. It is a challenge, an adventure and the right balance of risk/reward to keep it interesting ; )
Whether ABS is worth it depends on the type of rider you are. If youre the type that is easily distracted, has a hard time distinguishing from weather conditions/ice/moisture/grit on the road, knowing proper following distances, understanding the lean angle & traction relationship or the million other variables that come into keeping you alive than ABS might be beneficial to you.
I've tried to adopt certain behaviors to allow more time to react to any given situation. One of them being, riding with my right finger resting on the front break lever. It allows more time to react while also ensuring I don't mash the brakes if my "fight or flight" survival instincts kick in.
IHMO I think ABS has little usefullness on sportbikes. Harleys, Gold Wings and other big bikes benefit more from it. Like others have stated, track bikes gain nothing from ABS, rather they take away lever feel, feedback and even extend braking distances. ABS wins for new riders, distracted riders and extreme weather conditions. Really it comes down to knowing your capabilities as a rider. Just thought I'd share my feelings. Best of luck!