I've noticed on UA 917 IAD/SEA, which has operated on a 3 class intl 767 for a while, that the meal service is slightly different between C and F.

The choice of entrees isn't exactly the same, and for dessert F gets ice cream while C gets the traditional domestic F cheesecake.

As others have pointed out, F also has the personal tape readers, for what it's worth.

I'm quite surprised that UA bothers serving different meals in C and F on domestic flights. I'm not quite sure who'd actually buy F--except for those passengers connecting to/from intl flights. I wouldn't even upgrade to F on the 767.