What really started confusing me was when some of my Japanese friends would actually say 'wo' when they were reading something because I always thought it was just pronounced 'o'. One of my friends said that they read it 'wo', but in speech they say 'o'. So, whenever she'd read aloud, she'd say 'wo'. And sometimes I'd hear 'wo' out on the street. Then again, I find it easy to get confused when studying Japanese.