a) Americans do it regularly, other countries hardly at all
b) I'm not British
c) I always say vacuum for vacuum cleaner
d) Yes I say 'Thermos' but Thermos is closely associated with the function of the device (as i'm sure you're aware, knowing what a thermometer is) and also a shortening of 'thermal flask' which also allows the word to be used for flasks which perform the same function but with solid insulation rather than a vacuum.