A bit off topic, but it is a force as far as most physicists are concerned (albeit a "fictitious" one in that it does, as you say, originate from relative rotation of different co-ordinate reference frames), as it must be considered in dynamics calculations in a rotating frame. For example, a stone dropped perfectly vertically from a helicopter at the equator in totally calm conditions will experience the Coriolis force and thus drift slightly eastwards. If you ignored it, experiments wouldn't match your theory. Therefore it is a "real" force