An interesting thing about the Casimir force is that there is a derivation due to Lifshitz that doesn't use the concept of a quantized electromagnetic field; it

An interesting thing about the Casimir force is that there is a derivation due to Lifshitz that doesn't use the concept of a quantized electromagnetic field; it uses zero-point fluctuations of the charge distribution in the plates to get the same result. So it's not clear that the casimir force is direct evidence for zero-point field fluctuations. There was a nice paper a few years ago deriving a casimir-like force between (if I'm recalling correctly) a pair of coupled resistors/inductors. I can't find the reference right now, I'll post it later if I can.