I think that the whole email thing is a real conundrum. On the one hand a system that allows someone to send you a message directly is a great thing, on the other hand its terrible because you can end up with spam. I think that to harvest emails from a pure public commenting system is not the way to go. If a visitor wants to receive emails then let them sign up as a specific action not a side effect.

Generally email works as it is the lowest common denominator push system but that doesn't make it a 'good' system. I am personally surprised that pull systems such as Twitter have not taken over for this reason as with those you can choose to consume whichever lists you want. Anyhow I guess that is a different topic.....