At the WIPO meeting in December 1996, the consensus was that mirroring ran afoul of copyright and license issues, and that caching did not. Caching was deemed an automated (no human intervention required) response to demanded traffic, and mirroring was considered a proactive human act. I believe that there was a formal recommendation to this effect. Should the constituent bodies of WIPO agree with this notion, we could see civil law supporting it as early as 2007 (in the United States anyway). On the other hand if someone invokes the WIPO recommendation in defense of a civil suit (brought by a content provider who was losing advertising revenue) and wins, then the effect of the WIPO recommendation would make it into the law books even sooner. Note that RFC 2227 does more to resolve this issue than the WIPO recommendation does, since once it has been widely implemented, the content people are largely just going to put a restricted rights legend on their text to the effect that all copies must be unmodified, especially including the ad anchors, and that RFC 2227 must be implemented on all servers who hold such identical copies. The content people know that they will benefit hugely from caching and mirroring and anything else that offloads their web servers and primary links without requiring expensive mirrors and Cache Directors and whatnot. But at the moment the ad revenue they lose is worth more to them than the cost of doing their own mirroring.