well, i saw a documentary some years ago, it was about subtitles in bulgaria. and i was shocked to find out the main person making the translations for national tv and movies for the cinema was a single grandma in a dark room. and now that you mention it, i only ever had minor complaints about subtitles i saw on national tv and in the theatre. i never watched much cable so i can't comment on that. but as far back as i can remember, subtitles i've downloaded online have always been terrible, no higher than a 6/10 on the translation scale.
i still remember the worst translation i ever saw, it was for blade trinity. they were barely in the ballpark of what was being said. it really was amazing, i think the person making the translation understood about two words per sentence and then made up the rest