Microchipping is from all outward appearances not a painful experience. Dogs and cats receive them in the scruff of their necks usually or a bit lower down and it is much like a vaccine but as someone mentioned in an earlier post, a larger gauge needle is used but not that much larger. I've seen cats and dogs receive these and they don't even flinch. If it were for any other reason other than i.d. I wouldn't be for it but it helps get lost animals home so I think it's great.
I think the tattooes in the ear are a good idea as well. In this location they usually don't get covered by fur providing they are placed high enough up on the ear flap and that they are done well (i.e. legible). All vet clinics and shelters have a list of the codes used for tattooes so if a person finds a cat or a dog and calls any clinic or shelter, the code can be looked up to find out which vet clinic or shelter did the tattoo and then from there the owner can be found.
I run a website for lost and found pets and one of the things I usually tell people is to make sure they keep their contact information current with the hospital or shelter that actually did the tattoo. If the family moves and forgets to update this information the tattoo becomes entirely useless.

I am 100% against piercing and tattooing for cosmetic reasons (designs or words that are not used for i.d.). The piercing could lead to infection as others have mentioned and if a ring was used instead of a stud it could get caught on any number of things, including the animals own claws and could rip the ear or whatever part of the body is pierced. It would be so selfish to turn a pet into an accessory like that.
p.s. this is not directed at you Buttercup132 but just at the idea itself.