A prominent member of the ACM asserted to me that copyright assignment and putting papers behind the ACM's centralized 'digital library' paywall is the best way to ensure their long-term 'integrity'. That's certainly a novel theory; most computer scientists would say that wide replication, not centralization, is the best way to ensure availability, and that a centrally-controlled repository is more subject to tampering and other mischief than a decentralized and replicated one.
This is deeply ironic, because ACM bestowed both a Best Paper award and an ACM Student Research award on Petros Maniatis, Mema Roussopoulos, TJ Giuli, David S.H. Rosenthal, Mary Baker, and Yanto Muliadi, 'Preserving Peer Replicas By Rate-Limited Sampled Voting', 19th ACM Symposium on Operating Systems Principles (SOSP) , Bolton Landing, NY, October, 2003. for demonstrating that the 'prominent member' is wrong and Matt is right.
Even just thinking of the economics alone, and not of the systems issues, which preservation method would you rather trust? The prominent member's, which depends on the ACM's ability to extract rents from the scientific community into the indefinite future? Or a proliferation of copies in many repositories all over the world funded in diverse ways?