Well you can find some anecdotal stuff on the internet:
-it seems to be affective
-if the silver particules or to big and the parts per million ratio(ppm) is high there could be a chance of Argyria. I personally think that chance is small.
-if the silver particules or very small (nanoparticles) they could be potentially harmfull. After GMO, nanopartictles seem to be the next evil. read: http://www.reuters.com/article/idUSTRE60700H20100108
Smaller particles and low ppm seem to be more effective.
I wouldn't take it on a regular basis, only from time to time.