Yes Barbara people really do treat thin people differently. I was really, really shocked.
I lost 5 stone quite quickly and was appalled at the difference, never having realised quite how badly fat people are thought of by some.
Interestingly it was women who treated me differently - not men.
I'm considerably better looking thinner so that make make a difference in its own - I know that there are studies showing that people respond better the prettier you are.