I came across this recent research on the effect of qigong practice on Fibromyalgia. While the research was done using a specific set of qigong practices, the principles behind many common qigong sets should give similar results.
You can read the abstract here:
http://www.lightsource.com/ministry/winning-walk-tv/
http://arthritis-research.com/content/14/4/R178/abstract
and the full article here: