I previously published a post Haloscan commenting system for your blog (click BACK button to get back to this page) in response on how to get the email address of commentator. I stated that this is not possible with Blogger commenting system, but sisea of Sisea (This is a Chinese blog) says it is possible if you receive notification of comments via gmail. I tested this with Good Hobby Ideas, set the blog to receive comment notification by a gmail address, made a test comment, and found that it was true. See screenshot below (address partly blanked out for privacy):
I would expect you would also be able to get the email address if you choose to receive comment notification via other email addresses like Yahoo, and I hope to test that soon and update this post. I missed this because I moderate all my blogs, and it is not possible to get the email address of the commentator in the email notification for comment moderation. Since I already get notice of a comment made, I saw no necessity of getting comment notification. Anyway, many thanks to sisea for the alert.
Update: 11 January 2007: Apparently, something has changed since the last test. I made a few test comments and found that one can no longer get the email address of commentator even if one set to receive email notification via Gmail.