Hi James,
You asked:
Registering under pseudonyms is one method I have considered (and noted in other posts). But won't it have the same problem Timothy Takemoto noted in his 27Apr05 post?
Given the following quote from the Moodle Admin Configuration screen (underneath the NoReply email box) then if the email is visible in forum emails after setting it to be hidden in the user profile then there's a bug somewhere (or possibly just an unwanted interaction with Timothy's modifications).
Emails are sometimes sent out on behalf of a user (eg forum posts). The email address you specify here will be used as the "From" address in those cases when the recipients should not be able to reply directly to the user (eg when a user chooses to keep their address private).
I will test this and report back.
edit: our own 1.5 test Moodle does this correctly, and I've just hidden my email in my Moodle.org profile so if you are reading this as an email you should be able to see my name, but not my email address, if I changed my name to something anonymous then a fair degree of anonymity (at least between participants) seems achievable.