Hi Chris,
For what it's worth, in the Pylons Project, we decided to continue requiring the signing of a contributor's agreement (more or less the same contributor agreement as Zope requires). But instead of signing via paper, we ask that folks "sign" the contributor agreement by adding their name and date to a CONTRIBUTORS.txt file in a git fork of each repository they wish to commit to (e.g. https://github.com/Pylons/pyramid/blob/master/CONTRIBUTORS.txt). The CONTRIBUTORS.txt *is* the agreement, and the pull request serves as proof that they agree to the contribution terms it outlines.
I'm not 100% confident that this will serve as watertight proof of agreement in a well-funded court challenge. But it's a lot easier on the contributor and on the organization. The contributor doesn't need to use a fax or lick a stamp and wait, and at least if they're checked in they're fairly durable and have lots of backups (it would be very impressive if the ZF would be able to produce all the paper contributor agreements that have been signed over the course of Zope's existence on demand).
Yes, I remember "signing" the Repoze repository agreement in a similar way a few years ago. I liked it because it was convenient, sure. But as you say, I doubt it would hold up in a court. Speaking of those paper contributor agreement availability, you'd be surprised. I have them all in 3 large binders, for every signer the latest agreement they signed. jens