It's rare that a science fiction setting assumes that technology less effective than in the real world. That, or the medical community has been hiding the side-effects of current implant technology from us. After all, there are (conservatively speaking) tens of thousands of people out there with pacemakers, artificial joints, cochlinear implants, skeletal reinforcements/repairs, and other assorted types of implanted technology who are overdue for some nasty cancers by now. A number of them are friends or relatives of friends of mine, so it's going to be hard to break the news to them. i tend to go with the presumption that most advanced cybernetics are nearly imperceptible to casual scrutiny and are only employed when certain types of augmentation are desired that can't be achieved using less maintenance intensive organics. Man-machine interfaces, certain types of sensory agmentation and similar enhancements would be likely candidates. Of course it's not hard to imagine that installation/maintenance costs and social pressures would discourage obvious or excessive cybernetics.
On a related note, wired.com recently had some interesting articles on recent advances in the area of vision replacement/prosthesis.
-m[arcuS]