With a network of mirror sites where the data is shared on a many to many basis the problems of consistency are proportionately increased. If such data sinks were set up as nodes on the network they would benefit from a proper form of accreditation on the part of appropriate authorities in order to ensure that appropriate standards are set, maintained and guaranteed. Archiving also faces technical issues and these are huge. The electronic world consumes standards and data formats with unprecedented voracity. Different word processors and even different versions of the same word processor can be quite incompatible.
Much material is platform dependent.
Despite some bold pronouncements, it seems to me quite implausible to create a sort of working museum of hardware and software to keep information available in its original context - and even worse to have to do this at multiple sites around the globe. The only sane course is surely regularly to migrate material forward to new platforms to maintain not just the data but ease of access to it. This does carry risks of losing some data or at least nuances in the data, but this seems more realistic than assuming that we can indefinitely maintain the past. In passing, here one might mention that URLs may prove as ugly a problem to manage as they are to look at. Many of the draft papers for this conference cite URL's.