"This, of course, lead some in the patient community to wonder if the early studies wanted to find a virus."
This comment begs the question whether patients understand the scientific method.
In a scientific study, at least in those that can be trusted, the investigator(s) hypothesize a condition. I.E., do people with CFS exhibit any evidence of retroviral DNA in their blood? They then design a study that will either confirm or deny the existence of such retrovirus particles in the blood collected from their selected cohort. In a perfect world, the cohort would be selected prior to the hypothesis. Sometimes that doesn't happen, and it can indeed muddy the waters if the cohort is selected after the hypothesis is made.
However, it is my understanding that the WPI study, at least, had a group they were performing tests on prior to their XMRV discovery. So the selection effect - that is, selecting study subjects to influence the outcome - was not a factor. In fact, I believe the WPI were as surprised as anyone else to find that indeed there were retroviral particles in a large number of study participants. Maybe they were influenced by earlier work by Dr. Elaine DeFreitas to state the hypothesis. But I doubt they expected - or wanted - to find a retrovirus, one of the most difficult illnesses to treat, in their blood samples.
I cannot comment on other reports about finding XMRV, since I haven't studied them. It is hard enough for me to go through even 1 report. But I think it is important for everyone to keep the over-all scientific method in mind before commenting on whether a study is valid or not. Not replicating the exact test protocol is a definite way to dismiss a follow-up study. That's about as far as I would go to dismiss work done in other labs.