The 763-domestic I was on recently had a changing table.

As a relatively new father (7 mos), I really like to use the changing tables. It is much more private. However, on a recent 757 trip, there was no such changing table. The flight attendant said to change on the floor outside the lav, which didn't seem much better than at my seat in terms of cleanliness. If they have changing tables, I will use them. But otherwise, where else is there to change?