I know, I was sceptical too. It took example after example of great results on myself and others to convince me it worked. I grew up very scientifically minded and to be honest, Reiki can be very powerful and it still surprises me.
Even though we can't see or accurately measure the human biofield (at least not in a way that the scientific community accepts), there are studies on the benefits of reiki and energy healing. And I'm not talking about the many unscientific studies either - these have been published in PubMed! Basically they concluded that energy healing is an effective complementary treatment for a multitude of conditions - a pretty amazing conclusion for something published in the mainstream medical community.
It has been demonstrated to:
That last study was via distance healing, showing distance is no barrier to the benefits of energy healing! Obviously it doesn't replace the need for surgery if it is required, but it is a very powerful healing modality that has stood the test of time.
Links to many more studies are available at http://biofieldhealing.com/scientific-studies/
Of course the only way to really know something is to experience it for yourself. It even works via distance (strange but true!)