This Nature article, in which a group of scientists and ethicists come out in favor of allowing healthy people to take cognitive-enhancing drugs, has gotten a lot of news coverage, but it's definitely still worthwhile to read it for yourself.
The authors go pretty far out on some theoretical limbs--making the case that brain-stimulating drugs are no different than sleep or education and suggesting that someday it could be mandatory for surgeons to take the pills if they were proven to improve outcomes. But they build a compelling argument (and a lot of curiousity--would this blog post be vastly more intelligent if I had popped an Adderall beforehand?).
The article also puts a lot of responsibility on physicians, noting that they are already pushed by some healthy patients to prescribe the drugs (anyone want to comment on their experiences with that?). And, in the end, the experts want docs, or their representative organizations, to decide this tricky issue:
"It would therefore be helpful if physicians as a profession gave serious consideration to the ethics of appropriate prescribing of cognitive enhancers, and consulted widely as to how to strike the balance of limits for patient benefit and protection in a liberal democracy."