Public email [more ideas]
What I usually understand by 'idea' is something along the lines of 'novel solution to a difficult problem'. In this case this definition can be safely disregarded, as there isn't any problem, solution or novelty here... [There is a serious need for an irony sign in written language]
The www has enabled unprecedented forms of narcissism on one hand and voyeurism on the other. People write about the most mundane and trivial matters expecting other people to spend time reading it. 'Waste time by watching other people waste time' has become a viable tagline of web startups.
People blog about events in their everyday life, they publish the list of their friends and recently even write one-liners in status messages about what they are doing 'at the moment'. Clearly there is a need for even more self-expression and mixing of the public and the private. So why not a public email ? People could automatically post online the emails they send and the responses they get, others could watch the dialogue evolve, witness deals being done, relationships forming and unfolding. They could comment on messages, point out typos, suggest more nuanced formulations, give advice, predict responses, 'collaborate'. To protect privacy, names could be obfuscated, but on the long term the real fun would be in following both 'sides' of the story, an exchange of letters between two parties and the preparations, considerations that went into it from each sides.