Good points all.

With all due respect to Kevin and while absolutely NOT trying to insert any kind of pun here, I'd be more worried about some kind of backdoor entry into society.

Some corporation (why does Coke spring to mind?) might try to convince young people that such implantation is the "new-cool-thing-to-do" - that doing so would include fantastic benefits like discounts on products or the accumulation of points which could be redeemed for products. They would then make a competition to see how many scanning points around a city they could 'hit'. A great way to study the mobility habits of the generation with the greatest discretionary income.

Besides, didn't Schwarzenegger's character in "Total Recall" have something like that (albeit much larger) implanted in his brain which he quite painfully extracted thru his nose?

Wreck'd him? Damn near killed him.