I think it's early days to be worrying much about artificial sentience while there is still a lot of useful stuff to be done in artificial intelligence. While tool choice (eg fuzzy logic) and hardware substrate (eg memristors) will undoubtedly prove more or less useful over time, the general evolutionary approach as described by cjameshuff seems to be about right.
I think the behavior, if not verifiably the inner states, of machine intelligences will to us as observers become more sentient-like when we see systems that are maximizing toward a set of modifiable goals, able to select for and burn in more valuable experiences as we do via hormonal mechanisms, and ultimately seek to predict as much as experience in order to simplify immediate processing requirements. Though it would not be a full-blown advent of sentience, perhaps, I would still be tickled if a functioning system decided that energy is going to be more expensive in future and designed its own systems or those of descendants to enhance survival by using less energy. When we get the articles authored by machines about Robot Dieting in People (er, Machine) Magazine, we'll know sentience is coming along fine.
Calm down, have some dip. - George Carlin