Future problems in the determination of "prior" art?

In the article "Public Access Failure at PubMed," [313 Science 43 (7 July 2006)]:

"The policy also allows posting of papers that differ significantly from the final published version, which has the potential to create intellectual property issues as each public disclosure of the research represents prior art in the eyes of the law."

IPBiz is separately concerned about "early drafts" which appear on the internet and then later submerge, as is the case with some law review articles. Further, in the case of the NAS report on patent reform, the early draft contained some arguments which did not appear in the final draft.