CDMA networks (for example Verizon and Sprint in the US) have always been "SIM-less", and I've always felt one of the strengths of GSM over CDMA was the whole concept of an interchangeable identity SIM, from this perspective it seems a backward step.

Networks like Verizon which don't use SIM's rule what phones you can and can't use on their network with an iron fist. If you want to buy a phone on the open market and put it on their network and they don't want you to, tough luck. Without their co-operation to register the unique device identifier of the phone on their network, there is no way to get it working.

A compromise perhaps would be to have both a nominally empty SIM slot and an embedded "SIM" giving the best of both worlds, however the cynic in me worries that acceptance of such a feature is the slippery slope towards losing the SIM slot entirely in models one to two years later...