Actually, I used to have a similar ability as well, although that was primarily for life experiences + written material (came in handy on tests--read once-write anywhere, heh). It faded and largely disappeared sometime during high school. I feel I compensated fairly well afterward, so the loss doesn't bother me too much. Not that I wouldn't be interested if I found a way to get it back, though.

It seems different people may experience changes in this type of memory at different times. Maybe those adults who are considered to have really good memories just never had their childhood mnemonic abilities fade over time.