The idea of somebody with a scanner walking down a row of people and reading records from their bicep seems like it ought to be nefarious, but I haven't been able to think how. You could just as easily collect the data from a computer system or a filing cabinet.

There is at least one employer in the US who RFIDs its workers (this hit the news last winter). Ostensibly for secure access to areas as I recall, but one could also use it to monitor bathroom break length, etc. Perhaps not hugely different from badge tracking in that respect, but it's one step closer to enabling total surveillance.