good stuff! simple and obvious steps that help prevent, i would guess, 90% of abuse of email addresses. most people i am afraid are too complacent about the issue and probably unaware of unmindful of the proliferation of spam and similar junk on usenet, the very reason for the popularity of mailing lists today (after all usenet is a much better way to conduct these forums).
the next level of exploitation (if it hasn't started already) i would guess is subscribing to a list to harvest subscriber addresses. this, and other forms of collecting addresses from mailing lists (and list archives) is quite powerful, for not only do i have an email address that i know works, but often the list i harvested the address from tells me about the person's interests.
--ravi