Some things that are not exactly errata, but which do need to be clarified:
A Magical Focus that is applicable to an enchanted device, does that apply when you are investing a power into the device even when the Focus does not apply to the power? If it does not apply, then why does the Confraternity of Roland (HoH:MC p121) intiate a focus in Swords?
Exactly what is needed for Sense Holiness and Unholiness to Penetrate a demon's Magic Resistance? The text implies it is easier than when used against and angel that is trying to stay hidden, but the language is unclear on exactly how.
How to handle the cases where the background of a character includes two different Magical Foci. For example a magus of House Tremere with Mythical Blood. There are several possible ways to handle this conflict, but no official way that I know of.
When Wizard's Communion is used, do all participants need to cast it as a regular spell or not?