I have some experience with Reiki in a few different ways.
First, my father is a Reiki Master and swears by it. He's an 85 year old conservative, non-new age guy, but has studied Reiki for 30 years and thoroughly believes in it.
Second, I have had several Reiki sessions with a couple of Masters and although I was a skeptic, I have to say there was something really going on while I was being "energized". After a few minutes, I felt so relaxed in mind and body that I was amazed.
Third, I used to work for a newspaper and I wrote an article about Reiki. I interviewed a medical doctor who used Reiki in his practice (he's a surgeon), two Reiki Masters (not my dad), and people who have used Reiki for everything from drug addiction to stress to pain, and every single one said there was some benefit, whether great or small.
One thing to look out for...most Reiki practioners believe in the human kindness aspect of it and don't charge a lot for services. Their fees are supposed to be to help them continue their education of Reiki and not to get rich off people. So if it costs a lot, the practioner might know how to do the service effectively but their "soul" isn't in the "giving" mode. Find one that practices in that spirit of giving.