A large number of CFS/Fibromyalgia patients have been found to have the XMRV Retrovirus:

http://www.nytimes.com/2009/10/13/health/13fatigue.html

Testing is only being done in clinical trials right now, but this is the most exciting news I've heard, like, ever. My dad has suffered from CFS for nearly 30 years, so I am extremely happy to hear about this new development!

I'd say it's not enough to be linked as not everyone is tested positive for this, a lot of other illnesses and such go along side with M.E.

Agreed. To tie CFS/ME down to one virus seems unlikely at best. Here's hoping though.