This is a brill idea but I don't think using IP address as the seed will work, for the reasons given in the post ("Possible confusion"). pseudomonas' suggestion of cookies would work for my computer which has a different dynamic IP address from yesterday, but not for someone who posts from different computers at different times, and if you're on a public network the cookies will disappear at the end of your session, or it might be nobbled so as not to accept cookies. I'd like to see identicons as part of the named anonymous option, so people could put in an email address which wouldn't be shown to anyone but would generate an identicon, or get a cookie-based version otherwise.