"The typical American will have at least a dozen computers on his body, in the form of credit cards, rings and brooches. They'll be networked, and they'll get us through security checkpoints, monitor our vital signs, and provide GPS-style directions."

As for getting us through security check points, since Kurzweil did not predict that terrorists would bring down the World Trade Center in 2001, he also did not predict that the main bottleneck in getting people through checkpoints would not be credentialing but having people take off their shoes and carefully inspecting them for...something or other. And checking for bombs in their shampoo.

Devices for monitoring vital signs just did not happen, far as I know.

As for the rest of the computers on our body, it seems people prefer to have one broadly capable device for information, computation, entertainment, and communication, which is the cellphone (with iPhone best exemplifying the ideal of a single device with a broad range of capabilities). Having to compare and buy lots of little communication doodads worn on different parts of the body would just be an irritant (damn, wore the wrong earrings today, the podcast i wanted to listen to was on the other set and don't feel like waiting for it download again...)