Sam Ruby identifies the IP address of every person who comments on his weblog, as you can see by hovering over a name.

For message boards and weblog software I have developed, I won't reveal user IP addresses out of privacy and security considerations. Some users have static IP addresses, either from a high-speed Internet provider or their workplace, and could be vulnerable to hacking or harassment.

When I want more accountability for anonymous comments, I present a page of posts from a specific address without revealing the address.