Now that the riving knife is required on all new table saws, it might be a good idea to point out that these simple devices may not be quite the safety panacea that they have been made out to be. There is no doubt that a riving knife will increase the safety of any table saw. But we should not allow this to become one of those things where we think that having one will "make us safe."
One of the main things a riving knife is supposed to do is prevent kickbacks. Because the knife is basically the same width as the kerf, it will prevent "blade pinching" when ripping lumber. Pinching occurs when the kerf closes behind the blade due to stresses in the stock being relieved as it is cut. But, as often as not, the two halves of the stock will move apart rather than together. This can cause just as much havoc with control of the cut but will not be prevented or affected in any way by the presence of a riving knife. So the idea that a saw equipped with a riving knife is "immune" from kickback is inaccurate.
It is true that a riving knife will prevent contact with the outfeed side of the blade but it does nothing to block contact with the leading edge. So it is still incumbent on the user to pay attention to his hands in relation to the blade.
I am in total agreement with the idea that a riving knife is going to make table saw use safer. But the presence of one on your saw does not mean that you can ignore time-tested table saw safety measures.