Ah, finally got it running almost perfectly
A small detail, full name should be mapped to cn instead of sn, otherwise only the last name would appear
Now all I need is to figure out how to get the groups set up right..
Having all users be stuck on registered isn't perfect, as I'd like administrators to have administrator access in Joomla aswell
Gonna keep working on that one myself, but if anyone's got a suggestion, I certainly won't ignore it