I think, it depends on the region you play in.
If the group is based in a region, where you have universities, institutions for further education and the like, a librarian could come in handy. Especially if said person was working in this library for a longer time, he can find lots of older books, thereby lending a helping hand for all the other professions
I doubt, that such a character would be fun to play, but such a person would be a great NPC, IMHO.