How do each of you feel about the fact that it is impossible to verify that Bitcoin 0.9.3 is an official build, and therefore unlikely to have a backdoor that allows some nefarious party to steal your bitcoins?
Or, if there is a way to verify this, how does one do so?
Not sure what you mean. There's file signature hashes published at https://bitcoin.org/en/download . That file is signed with Wladimirs key.
Near as I can tell, 'Wladimir's key' is unverifiable as being Wladimir's key. Perhaps I am doing it wrong, but this is what I see:
host:dirname username$ gpg --verify SHA256SUMS.asc
gpg: Signature made Mon Sep 29 08:44:14 2014 MDT using RSA key ID 2346C9A6
gpg: requesting key 2346C9A6 from hkp server keys.gnupg.net
gpg: key 2346C9A6: public key "Wladimir J. van der Laan" imported
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0 valid: 2 signed: 0 trust: 0-, 0q, 0n, 0m, 0f, 2u
gpg: next trustdb check due at 2015-08-18
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
gpg: Good signature from "Wladimir J. van der Laan"
gpg: aka "Wladimir J. van der Laan"
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: 71A3 B167 3540 5025 D447 E8F2 7481 0B01 2346 C9A6