Last night I read a story by Greg Egan (hard sci-fi), about a society so far in the future that immortality is gained by having a device learn to be you. It basically acts as a secondary brain, mimicing everything that squishy mass does, but it does not degrade. Bodies are replaced every now and then, since clones can be grown in about a year. The story mainly revolves around a) the main character's questioning on whether he is actually the same person as before, and b) his relationship with his wife, and getting closer.

Now, I think the world will be dead and gone long before that happens, but if it did, I know for sure I would never get that done, because a) I am more the sum of the parts of me, but the parts still matter and b) WTF getting rid of your brain?

Even now we have devices basically taking over (phones, computers, pacemakers, diabetes control), but we are still separate. Once we start putting stuff in our bodies, how long until we no longer have control?