The entire book in which this essay appears is available here, for free.
It was also discussed on Less Wrong previously.
Oh, I didn't know it had been posted about before - since no post brought it up specifically - or that it appeared in The Mind's I, I hope that doesn't make the post altogether obsolete.
Great link BTW.
”Where Am I?” is a short story by Daniel Dennett from his book Brainstorms: Philosophical Essays on Mind and Psychology. Some of you might already be familiar with it.
The story is a humorous semi-science fiction one, where Dennett gets a job offer form Pentagon that entails moving his brain into a vat, without actually moving his point of view. Later on it brings up questions about uploading and what it would mean in terms of diverging perspectives and so on. Aside from being a joy to read, it offers solutions to a few hurdles about the nature of consciousnesses and personal identity.