There may be little things that didn't get picked up during their hours and hours of testing, but those will most likely be addressed quickly with a software update. In general I think you'll find Panther to be very stable.
My experience is that your concerns are unfounded. New Apple operating systems are extremely stable. You are much more likely to have bugs in new third-party applications and utilities than you are with MacOS X 10.5. Is it worth it? After reviewing the new Leopard video, I would say that Leopard is at least as big a step over Tiger as System 7 was over System 6. Apple could have easily called this version MacOS X 11. Is it worth it? Most definitely!