It took me the best part of three days to find the one word
in the MySQL Database: Multiple XBMC HTPC's with 1 Shared Library
thread to get the centralised database working properly; so I figure it's worthwhile putting the solution here. The word is "latin1
Initially, following the Lifehacker instructions looked like they worked, but I couldn't select Library Mode, and I couldn't show the "TV Shows" and "Movies" options on the main menu. It was all in the character/collation schema. It's now set to "latin1_general_ci" and it's all working fine (after deleting and recreating the relevent sources).
I assume it's all in the different representation of special characters between latin1
and my original selection of utf8