I think that in the first step, the mailing list messages could simply be further qualified with some keyphrases (one or more phrases which each contain one or more keywords that describe the issue in possibly increasing detail as in "workflow, customize", "xxx, x111, x222") by all, and maybe some of the more experienced ones could try to start the practice and establish some good examples of keyphrase structures. This annotation should of course take place already when messages are posted, but could be revised later in a database.
I think this is a noble idea, but I also believe that it would be very difficult to expect of folks. ;-) Open source software development and support is chaos. People can't even remember what day it is or whether they had lunch most of the time when they're developing software, much less how the Zope maillist taxonomy works. An explicit keyword list in email messages would be very difficult to enforce, and most folks wouldn't pay much attention. Now Bill's and Andy's idea where folks used an email client to post a FAQ explicitly might work pretty well.. this would work because individuals could do it without much fuss.
The second component would be some kind of rating - so that those who find a snippet useful or wrong could indicate that (but I am not sure how to do this so that there would be some kind of quality control in the quality control).
ZopeLabs has this. The Python Cookbook at ActiveState also has this. Thanks! - C