Answer:
Any technology presents advantages and dangers, as does nanotech. There are two different uses of the term "nanotechnology" just now. One deals with material reduced to tiny particles that have a comparatively huge surface area. The other, more exotic modality invovles the creation of tiny machines -- this last is not very far along as of yet.
n-AC (Activated Charcoal) is just as absorbative as before, but the increased surface area means that the overall absorption is at least one order of magnitude higher at the same gram dosage. n-Al (Nano-aluminum) on the other hand tends to catch fire. Aluminum burns at a VERY hot temp, and aluminum fires are nasty. Various other nano-compounds and elements present similar if novel reactions.
Nano particles could lead to health related issues.