Prayer

"The largest and most scientifically rigorous study of prayer's efficacy, the 2006 STEP project, found no significant difference whether subjects were prayed for or not, except some negative effects among those who knew they were receiving prayers."  (source)

It goes downhill from there:

The power of faith and prayer?

We believe that the research has led nowhere, and that future research, if any, will forever be constrained by the scientific limitations that we outline.

The benefits of placebos are well known but are a far cry from trying to employ psychokinetic powers to affect the health and well being of others.