I had upgraded my version of Mysql Server via the ports a few weeks back and usually ports is very good at addressing any compatibility issues bumping up the versions. A quick read of UPDATING had not flagged any real concerns, but on the reboot Mysql was steadfastly refusing to start. No obvious error messages where thrown and it just silently refused to budge.
Googling presented several solutions, but none palpable (wipe config and dbs and start again). However one suggestion was to check the {hostname}.err file contained within /var/db/mysql and lo and behold a quick TAIL {hostname}.err displayed the error that I have been missing. Namely that query_cache_type=0 and query_cache_size=0 had been deprecated starting with v8 and needed to be deleted from my.cnf file.
Fixing the my.cnf file and a quick service mysql-server start restored my Databases and we are back up and running.