Saw a great sci-fi film about identity fraud - don't quote but I think it was called Gattica. In this world, everyone's genetic make up is known and scanned everywhere you go, just to get through the door at work. People with "inferior" genetics are blatantly discriminated against, and our hero wants a promotion at work that he's not allowed due to being "inferior". The story is about how he teams up with a guy whose genetic materials he borrows - hair, urine samples etc. to present for various checks, so he can get the promotion.
Already the insurance companies and hospitals are talking about favoritism to people with a particular gene set, or tax bracket in some places in the world, and you can store this kind of information in a bar code or implant. Not to mention all yer bank details, criminal records, who you send emails to...
If people start getting these implants put in (and I'm sure it will happen some point), what percentage of the population need to have one for them to start fitting them at birth in hospitals? They'll start with medical reasons, then tracking criminals, then tracking suspected criminals, then asylum seekers, before you know it there'll be more people with them than without.
This sort of stuff really frightens me. I shudder to think how all this could be misused, and not just by the government. Any half-arsed hacker could get hold of the information.