On my Mac’s Activity Monitor, I’ve seen the System CPU usage jump up to 30% or more during an update of the battle.net app, and the User CPU to 40% or more. And right now during a WoW update, the System CPU usage is around 25-30% and the User CPU is around 40-50%.
The battle.net app itself doesn’t seem to be using much CPU but the Blizzard Agent does.
I don’t think its supposed to be using System CPU at all. User CPU I can understand (though is it really supposed to be that high?).
I’m not sure it matters, but this is on an Intel Mac.