Since everyone seems to have an opinion about the iPhone 5s having a 64-bit processor, here's mine.
In the immediate future, this will make zero difference for consumers. Applications that ship today will continue to be compiled as 32-bit, so that they can run on all the other iOS devices as well. Since the iPhone 5s is likely to be faster than all those other iOS devices as well, there's little point right not optimizing an application for the iPhone 5s, everything that runs well enough on an iPhone 4s or iPhone 5 or iPhone 5c will run well enough on an iPhone 5s as well. Optimize for the low end, and the high end will take care if itself.
In the medium term, there will come a moment in time when all supported iOS devices have 64-bit support, with Apple dropping support for 32-bit devices. At that point, the iPhone 5s will be the oldest supported iOS devices, and the iPhone 5c won't be supported any more. Indirectly, that means that the iPhone 5s will have a longer useful life than the iPhone 5c, and since the difference between 32-bit and 64-bit is qualitative and not quantitative, it's possible that the useful life of an iPhone 5s will be more than one year longer than that of the iPhone 5c. Users who care about how long they can keep their phones before being forced to replace them because of obsolescence could consider the more expensive iPhone 5s over an iPhone 5c on this point alone, regardless of the other differences.
Finally, 64-bit support in the iPhone 5s is a great stepping stone for developers. Even though deploying 64-bit-only applications might not be practical for another few years, it's never too early to make sure that code compiles for 64-bit targets and passes all the unit tests, to run microbenchmarks, and maybe even for some dogfooding. In the long term, I can't rule out that Apple would remove 32-bit support entirely and would therefore mandate 64-bit applications, and it's probably easier to get ready on an ongoing basis than to go through a 64-bit fire drill many years down the road.