I just noticed that you can get someone's profile by username instead of by userid. For example, to get my profile I just go to:
http://www.antionline.com/member.php...username=katja

Still, I'm not sure if AO really meant users to have access to the memberlist in this way... The default way would be through the userid like this:
http://www.antionline.com/member.php...&userid=198056

Still, I consider this a cool feature.

Then again, passing information like this through the URL might not be the safest way.