I just want to say I think the ideas presented in this blog are excellent.
I love that spells will be something fundamentally different from "normal" attacks. One of my biggest complaints with almost all (fantasy) MMOs is that magic is just another type of ranged attack, usually with slightly fancier graphics.
Having them be something powerful but limited and costly should go a long way toward making magic magical again.
Also I really like that a spell book is a unique strength and weakness and the drive to acquire new spells should lead to all sorts of appropriately wizardly behavior.
Finally I'd enjoy seeing ritual siege magic and magic wards against it in addition to more mundane siege engines and walls.