Hope you got your dog back in good shape, Southplatter.
The chips in my dogs are between the shoulder blades, about the size of a grain of rice. They put them in with a big ol' syringe!
With a scanner, a vet can get a number, which is in data base of one of three companies and will give the pet's name, and owners info as registered when the chip was placed. (If you move you can tell your vet, or get online and update your contact info). Pretty sure these are not GPS technology. Very handy if the dog shows up at a shelter.
I have seen GPS equipped collars on hunting dogs on TV -- pretty cool. Last week on "Lady Hoggers."