Just to add some perspective from the outside world (I.e. Not America). In Italy sliced bread never really took over common bread. Yes we make toasts, and yes, we have sliced bread, but that's usually some industrial, over-processed bread loaf that you'll never find fresh at a bakery.

Here in Germany, were I live now, it's a mix. Common bread everywhere, but you can slice your own loaf at the supermarket with a terrific automated spring-loaded circular saw machine that's very cool to operate.

I just want to point out that "the best thing since sliced bread" is a sentence culturally linked to the U.S. conception of bread. I point that out because I had conversation with American friends in the past who were surprised by the non-universality of this sentence (as often happens with other cultural references).