Sounds cool, and usefull.
potential roadblocks to over come:
What stops a spammer from creating a new account?
Banning IP's works, but many of my members come through a proxy server. I ban a lot of people with one IP.
Cookies would work but too many people know how to clear cache and cookies.
And Ill go you one better. Along the lines of the Kudos thing. Let people build points. Good for special titles, Avatars, cookie of the month, discounts off merchandise etc.
