Long after email announced dead mailing lists still constitute for me the main source of information in the most important for me topics.
Their publish-subscribe nature and the universal availability makes them an ideal tool for many communities of practice. The archives of many mailing lists represent major source of information on many topics - but the exposition of this information is far from being perfect. I can see one small improvement that would help a bit - the mailing list servers should put in the footer of the letter a link to the archived version of it. This would spare a bit of work for anyone wanting to publish a link to some interesting email conversation and in effect would improve the flow of ideas between www and email.