Posner on Fair Use. Regardless of which side of the issue you're on, you should really be reading Judge Posner's posts on fair use over at Larry's blog. From a recent post:

"With regard to the Patry-Posner proposal for creating a new fair-use defense for unauthorized copying of old copyrighted workers if the copier was unable with reasonable effort to discover the name and address of the current holder of the copyright, several commenters point out that one of the objections to the pre-1976 system, where failure to renewal forfeited copyright, was that people often just forgot to renew or botched the renewal application. No doubt there were unfortunate such incidents. But in general forgetting to renew or botching the application is pretty good evidence that the copyright had little remaining value. People are careful with property that they think valuable. Failure to renew even if inadvertent is pretty good evidence of lack of value."