Seattle-based designer Gina Miller has come up with a piece of plausible speculative technology. Her Dermal Nanotech Display is worn on the back of the hand, where billions of nanomachines planted just under the skin provide a linked information display. Miller's model (including animation) focuses on personal biomedical information; in principle, there's no reason why the same display couldn't also interface with an external network.
Real implanted displays probably won't be exactly like this, but I find these kinds of speculation projects to be very useful for helping to frame what we do and don't want with emerging technologies.
Not so much with a display. I'd rather see something more like a transdermal tatoo with a nanotech "smart ink" (something like a bio smart dust) that is transparent to the naked eye, but visible or audible to a scanner or viewer. Too much intelligence required in making a transdermal display; put the intelligence in the interpretive device so that the appropriate party reads it (a doctor or other trained medical professional) versus everybody else that can hack a transdermal display.
Maybe the must have accessory for third string quaterbacks pressed into action.
A PDA sandwiched between the dermal layers--certainly a conversation starter but what about upgrades?
I grant Gina's idea might be built with advanced nanotechnology (The stuff the Foresight Institute and the CRN talk about not the stuff that Eddie Bauer or L'Oréal talks about.) and as such may be the last word in computing machinary--short of nucleonic matter. It may never need upgrading but that's all decades away. What do we do before then?
Given the constant need for upgrades and repairs in our less-than-nano-technology, jamming these things in you seems overly cumbersome. I'll stick with fyborg solutions, not cyborg solutions, thanks! I'd rather have an tee-shirt display than an animated tatoo.