Raymott
In most cases, as in the example I gave with the 'meal' sentence, the sense is essentially the same but I maintain that there is a subtle difference. 'Disappointed by' suggests something has happened that has dashed your hopes or expectations (in time line terms, a favourite of English teachers, it would be indicated by a vertical arrow); 'disappointed in/with' implies that you are in a state of disappointment because of something that has happened (in time line terms, a continous horizontal arrow). In practice, almost the same but with a different emphasis. Otherwise, they would be interchangeable in all cases, which they aren't.
So:
'I was disappointed by him' - he let me down (one instance)
"I was disappointed by him yet again." Is this possible?
I was disappointed in/with him' - no suggestion of an action causing disappointment;
Well, something made you disappointed in/with him. It's true that you could be disappointed in him because you wanted a girl and you got a boy - which was no action on his part. But 'in/with' are just as valid if there has been an action by him.
instead, this conveys a general feeling of disappointment.
If you have a general feeling of disappointment, why attribute it to him using 'in/with'? You'd only do this if the disappointment was caused by him - in which case, you would have been disappointed by him.