finally thought of an answer to the "upload your brain to a computer and live forever" thing:

the uploaded "you" isn't YOU. To use an analogy: if you have a match and light it, you have a flame. If you then use this flame to light a different match, you have two lit matches, or two flames. You wouldn't say they're THE SAME flame. You may say they're related, since one came from the other, but from the point of creation they are different flames.