So i had just purchased a license a few hours ago and just installed and converted IPS 18.104.22.168 over to xF and discovered one crucial error in the importer.
The importer is looking for seperate data that has been changed in 4.1.
In 4.0 I guess it was pfields_groups.pf_group_key, however in 4.1. the correct data is pfields_groups.pf_group_id,
So i had to modify my importer file (/public_html/library/XenForo/Importer/IPBoard40x.php) in order for it to succeed.
Now, Basically what I'm suggesting is to add another file to the importer, Say IPBoard41x.php and then just change that one variable and that way it prevents customers who have no idea what to do from having to search, They can just succeed the first time.
Was going to post this under Tips but the forums won't let me post in those sections yet.