Due to control bonuses from specialization and foci, it seems like magical attacks are disproportionately powerful compared to any other venue. Bonuses "to hit" are fairly rare in the system, except with magical practitioners. This gets to a point where a very powerful wizard's attacks are nearly impossible to dodge because of the control bonus on top of their Discipline when they cast. I am running a game with serious heavy-hitters on the NPC side and, as I was building the bad guys, became concerned at their damage potential.
My initial idea was to change it so that Weapon rating for spells took two shifts instead of one, like Armor. However, this hurt the PCs more than it did the powerful NPCs and also didn't address the "to hit" problem. What I ended up doing was house-ruling that the Control bonuses only applied to the roll for the purpose of controlling the Power summoned, but not for seeing if it hit. This retains the benefit of control bonuses in allowing you to successfully channel large amounts of power without it also making you hyper-accurate (and, thus, adding even /more/ damage from additional shifts). It also brings shields back to a level of effectiveness that, I feel, better parallels the books and closes the disparity between a powerful mage and a powerful physical combatant.
For example: Bob calls forth 7 shifts of Power and gets +4 for his Discipline roll. He has a +1 specialization control bonus and a +2 focus control bonus, so his Control roll is +7, just enough. However, he only compares the +4 to his target's defense to see if it hits.