[Michael Chandra]

Does a power focus add dice or add to effective magic rating?  That is, if I have 4 Magic and a rating 3 power focus, can I cast force 7 spells without risking physical drain (and other force-related effects and formulae following suit)?

In short, the fluff talk is raising 'effective' Magic, which as in-game mechanic solely has a dicepool bonus on your Sorcery/Conjuring/Alchemy tests. This means no impact on overcasting or PP, but also no stacking with Spellcasting/Dispelling/Conjuring/alchemicalstuff foci that also add dice. The math is that if you have more than ... 3 iirc?... different kinds of things you'd like a Focus on, Power Focus is superior.

[Cronstintein]

Hmm I thought that power focus vs drain issue came up the other day and we determined that it does effect drain.  I don't have a book in front of me to double check the wording but I was convinced at the time.

[Michael Chandra]

Definitely not the case. Didn't do so in SR3 either, and the phrasing hasn't really changed since SR4: It's just a dicepool bonus on any test that has +Magic in it.