Wow! Yet another article about "smart drugs" that's actually about stimulants! I give it one hour before people start mentioning Erdos and talking about amphetamines instead. (Edit: Yup, and now I'm getting downvoted.)

Here's a much better article about actual smart drugs (http://sites.google.com/site/thinkinginanutshell/nootropics), and its HN discussion (http://news.ycombinator.com/item?id=1211959). Sorting them in terms of risk & body load is a good idea, I think. He's not kidding when he says vaso-/desmopressin messes with homeostasis.

The racetams (piracetam, aniracetam, oxiracetam, etc.) are probably the least risky, though I've had the best long-term effects from getting enough sleep and exercise, eating reasonably well, and not spiking and crashing on caffeine all the time. If you want to try nootropics, be informed and careful, and address the obvious factors that may be messing with your concentration first. (For me it was sleep debt and too much caffeine.)