We discussed this study at length quite some time ago but unfortunately the thread title wasn't related to the subject and I can't recall it now, so it wouldn't be easy to track the thread down.
On that thread, the idea that chocolate might be beneficial for ME patients, and that this was a genuine area of research, was angrily dismissed by some, who saw it as belittling and ridiculous. But the most memorable part of the discussion for me was when one of those who was angry about the study asserted that nobody would seriously consider insulting people with serious diseases like AIDS and Cancer by conducting such offensive research - and I then found several pages of chocolate/AIDS research with a 30 second PubMed search.
I've found dark chocolate hugely beneficial but it took several years before I found a brand that didn't also contain various other products that are harmful to me because of my food sensitivities - caffeine, soya, dairy, nuts, wheat and gluten, egg...there are so many reasons why most chocolate products can be harmful to us. I'm posting this now because I've been meaning for a long time to share the brand of dark chocolate that I found so helpful:
Plamil Organics, Organic Dark Chocolate; Plamil Foods Ltd, Folkestone, Kent CT19 6PQ.
http://www.plamilfoods.co.uk/chocolate
Biophile is right, the polyphenols and flavinoids in cocoa are the subject of a great deal of research interest and the aim will of course be to identify the most beneficial compounds for human health, and sell them as drugs. But in the meantime, I'd strongly recommend anybody who hasn't tried a completely allergen-free dark chocolate to give it a try. It certainly made a big difference for me.