I am virtually musically dyslexic, myself.
I cannot learn anything purely by reading the score; I have to hear it, and then either learn it using both hearing and the sheet music, or just using the score as a rough guide and picking out most stuff by ear.
Therefore, if someone puts previously unseen sheet music in front of me and asks me to play it straight away, I am basically completely hopeless
(On the other hand, I have almost-perfect pitch, and can pick stuff out by ear pretty easily.)
Curious to hear what other people say!