Hi, fauyd,
I wish to avoid "debunking" at PF, so I won't argue with supporters of some "dodgy" claims mentioned below, I just want to provide a few relevant links for you.
As you probably know, Clifford M. Will, an internationally recognized authority on testing theories of gravitation (he is the author of several books on this and some much cited review papers), and other experts contend that Kopeikin misanalyzed the data of Fomalont. Their arguments are summarized at
http://wugrav.wustl.edu/people/CMW/SpeedofGravity.html. Kopeikin and Fomalont continue to insist that they are correct, but AFAIK they are almost alone in that viewpoint.
I add a general comment about lessons which can be drawn by inexpert observers: Kopeikin chose the unorthodox route of announcing his results at a news conference (to be sure, his news confereence was held during a general astronomy conference in Seattle, although I believe it was
not part of the official conference proceedings), rather than following the more sober and traditional route of writing and submitting a paper to a high quality journal in the usual way. Such a procedure seems to be something of a "warning flag".
To recall some other gtr-related incidents in the past two years:
1. one Franklin S. Felber, who apparently formerly worked in the U.S. Defense industry and who may have some kind of physics degree, formed a company called Starmark and widely disseminated press releases claiming discovery of a revolutionary spacecraft propulsion technique based on supposed "antigravity beams". But his eprints gr-qc/0505099, gr-qc/0505098, gr-qc/0604076 appear never to have been published (with good reason; Felber was terribly confused on several basic points, but his essential goof was mistaking coordinate phenomena for a phenomenon having physical significance, which led him to conclude, incorrectly, that moving objects emit an "antigravity beam" in their direction of motion).
2. one Alexander Franklin Mayer, who has apparently formed a company called Mirusoft, and who describes himself as a "cosmologist" (I was never able to verify that--- as far as I could tell, he apparently previously worked as a patent examiner, which might meant that he did earn some kind of graduate degree in some technical field) and who was very briefly a visiting scholar at Stanford, claimed that something was wrong with GPS, but he appears to have misanalyzed his data, and nothing seems to have come of his claims, which were widely discussed on the cranknet, but never published. Two mainstream surveys of relativistic physics in GPS are http://relativity.livingreviews.org/Articles/lrr-2003-1/index.html and
http://www.arxiv.org/abs/gr-qc/0507121
3. one Ronald M. Hatch, an engineer (he did earn an undergraduate degree in physics) who says he worked on satellite navigation for Boeing and other companies, formed a company called NavCom Technology and proposed (apparently by press release) his "Ether Gauge Theory", which has been widely discussed on the cranknet. Hatch, who is allegedly a member of the Natural Philosophy Alliance (a "fringe science" organization), also claims that NASA's model for satellite navigation resembles his own theory, not special relativity, and he has apparently claimed that the mainstream analysis of GPS above is wrong. These claims have apparently not been published except in such places as the "new energy" newsletter Infinite Energy Magazine, which was founded by cold fusion proponent Eugene Mallove (who has since died--- there seems to be a conspiracy theory regarding the manner of his death).
4. one Roger Shawyer, a microwave engineer, formed a company called SPR, Ltd. and inveigled New Scientist into publishing a cover story claiming that Shawyer had demonstrated what would amount to another alleged method of spacecraft propulsion which would have violated conservation of momentum. After an outcry from physicists, he released a crude "theoretical analysis" which was quickly and independently debunked by several physicists, including Greg Egan (best known as a science fiction author, but he is a physicist by training)
http://gregegan.customer.netspace.net.au/SCIENCE/Cavity/Simple.html. Another feature of this affair was that someone in the British government apparently approved giving Shawyer a sizable sum without first consulting a physicist to review his grant application.
From this list, I think the point about the importance of refereed papers appearing in top quality journals is clear. The remarkable feature of the Kopeikin affair is that he does have a previous record of respectable publications; a common denominator of many wild claims discussed on the crankweb is that the protagonists often have an unimpressive record of prior scientific publications, and often possesses somewhat dubious scientific credentials. (In particular, engineers are not trained to perform basic scientific research.) Another common denominator of many of these claims is that the protagonist has formed a company, perhaps to seek private investment in his schemes.