Today I was feeling particularly adventurous. Having reliable backups of all databases on hand, I decided to upgrade MYSQL to the latest point release 5.150.
My instincts told me this was going to be a semi disaster, but nothing so bad that it wouldn't be recoverable. Upgrading through Webmin 1.5 was a snap and it used YUM to handle all the dependencies etc.
All sites with small databases seem to have been migrated without any trouble. But larger databases did not like the business of being transitioned at all. Needless to say most databases did not get upgraded on the fly.