No his thesis is that it is possible that even a maximal upload wouldn't be human in the same way. His main argument goes like this:
a) There is no way to find out the universe's initial state, thanks to no-cloning, the requirement of low entropy, and there being only one copy.
b) So we have to talk about uncertainty about wavefunctions - something he calls Knightian uncertainty (roughly, a probability distribution over probability distributions).
c) It is conceivable that particles in which the Knightian uncertainties linger (ie they have never spoken to anything macroscopic enough for decoherence to happen) mess around with us, and it is likely that our brain and only our brain is sensitive enough to one photon for that to mess around with how it would otherwise interact (he proposes Na-ion pathways).
d) We define "non-free" as something that can be predicted by a superintelligence without destroying the system (ie you can mess around with everything else if you want, though within reasonable bounds the interior of which we can see extensively).
e) Because of Knightian uncertainty it is impossible to predict people, if such an account is true.
My disagreements (well, not quite - more, why I'm still compatibilist after reading this):
a) predictability is different from determinism - his argument never contradicts determinism (modulo prob dists but we never gave a shit about that anyway) unless we consider Knightian uncertainties ontological rather than epistemic (and I should warn you that physics has a history of things suddenly making a jump from one to the other rather suddenly). And if it's not deterministic, according to my interpretation of the word, we wouldn't have free will any more.
b) this freedom is still basically random. It has more to do with your identification of personality than anything Penrose ever said, because these freebits only hit you rarely and only at one place in your brain - but when they do affect it they affect it randomly among considered possiblities,
I'd say I was rather benefitted by reading it, because it is a stellar example of steelmanning a seemingly (and really, I can say now that I'm done) incoherent position (well, or being the steel man of said position). Here's a bit of his conclusion that seems relevant here:
To any “mystical” readers, who want human beings to be as free as possible from the mechanistic chains of cause and effect, I say: this picture represents the absolute maximum that I can see how to offer you, if I confine myself to speculations that I can imagine making contact with our current scientific understanding of the world. Perhaps it’s less than you want; on the other hand, it does seem like more than the usual compatibilist account offers! To any “rationalist” readers, who cheer when consciousness, free will, or similarly woolly notions get steamrolled by the advance of science, I say: you can feel vindicated, if you like, that despite searching (almost literally) to the ends of the universe, I wasn’t able to offer the “mystics” anything more than I was! And even what I do offer might be ruled out by future discoveries.
Scott Aaronson has a new 85 page essay up, titled "The Ghost in the Quantum Turing Machine". (Abstract here.) In Section 2.11 (Singulatarianism) he explicitly mentions Eliezer as an influence. But that's just a starting point, and he then moves in a direction that's very far from any kind of LW consensus. Among other things, he suggests that a crucial qualitative difference between a person and a digital upload is that the laws of physics prohibit making perfect copies of a person. Personally, I find the arguments completely unconvincing, but Aaronson is always thought-provoking and fun to read, and this is a good excuse to read about things like (I quote the abstract) "the No-Cloning Theorem, the measurement problem, decoherence, chaos, the arrow of time, the holographic principle, Newcomb's paradox, Boltzmann brains, algorithmic information theory, and the Common Prior Assumption". This is not just a shopping list of buzzwords, these are all important components of the author's main argument. It unfortunately still seems weak to me, but the time spent reading it is not wasted at all.