[globnomulous]

Peter F. Hamilton's Pandora's Star contains a wonderful variant of this thought experiment: in the future he describes, memories are editable; so it's possible to commit a crime, like murder, and then wipe all memory of it, so that you are, from your own perspective, innocent. The justice system, of course, says otherwise. The metaphysics (whether or not it's possible to step into the same river twice) don't matter. Technological advancement dictates the answer to the philosophical question about continuity of the self and guilt.