I don't usually sub-vocalize as defined in the poll. For people curious about what that's like, for me the closest analogy is reading a stock market ticker...words "flow across" my mental landscape

. I speed-read all the time so I don't have enough "time" to hear words.
I do occasionally hum to myself in a reading tone when reading (another kind of sub-vocalization). I do that with very dry technical books. It tends to annoy people around me. In those cases, I hear my own mental voice reading the books aloud. The audible noise I make is sort of "Mmm mmm MUH...hmm...MMMmmmnnnn...." Yes, it does annoy the heck out of people around me.
Very rarely, an author will write beautifully enough that I hear voices for each of the characters. For me, that's a sign of a superlative work. I have to stop my eyes at each paragraph break/dialogue change to let the inner narrators catch up. It makes for some strange situations when each speaker is not clearly telegraphed.