Best experience on a 767-300 was when when was subbed for likely a MD-80 on a LAS-ORD flight probably 10 years ago. I was shocked when I woke up the morning of the flight and saw my upgrade had cleared as a lowly gold, when I went to check the seat map it was obvious the substitution had opened up a bunch of seats up front.
As an almost 100% domestic flyer, it was my first exposure to an international first class seat. I remember the flight being delayed slightly since the ground crew as LAS was not all that familiar with the 767, and took a little to figure out how to load the baggage containers.
Other memory is from the movie home alone 2 where Kevin is apparently flying a 767-300 from ORD-LGA, while the rest of the family is flying a 767-300 ORD-MIA.