I think of each new version of the iMac as an individual entity. My G5 iMac, for instance, is the "rev B," and then along came the "rev C," but that particular iMac had a new distinguishing characteristic: the addition of the iSight camera, so in my mind, that became "the iSight iMac..." and now we've got our first version of the iMacs with intel inside, and so, yeah, I tend to think of those as the Core Duo iMacs because of course there are going to be future iMacs which will have other distinguishing characteristics and eventually other intel chips inside...
Well, actually, I tend to think of and call my iMac "sweetheart," but that's hardly the official designation!