I've set the Site Permissions for Extra User Info to "1" for Admins and moderators, but still all users seem to be able to see things like IP for every post.

It has to be something in your permissions in your CP. I have checked this on both my test board and my public site by using a test log in account and can not recreate this without setting the permissions to show that information to the user group.

Probably, I can't replicate it either now.

Hmm. My test user can't see the extra info. But a user who used to be an admin, before the upgrade, can. He is only in two user groups, and neither of them have any Extra Info permissions.

OK, I found the problem. The user is still a member of the Moderators group even though he is now a normal user. And the Moderator group doesn't show up on the group list for the user.

Removed the user from the moderator group in the db now, but he still sees the IP. Are there any more places the moderator info is saved?

Never mind, updated the user from admin member management and now it seems to work.