i haven't had any serious problems simply copying the files from one drive to the other.
if you are copying from Camera cards, then there is a priority to do a careful, verified copy.
otherwise, simple drag n drop, or copy & paste, is fine.
Carbon Copy Cloner will verify copies it makes, i believe. (takes longer of course)
also there is an article about checksum verification you could read, although its very technical:
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library.creativecow.net]
nick