Well before you get all perky... you cant BLOCK with a shield if you have magic in your other hand..
Also the shield spell in skyrim protects vs magic not so much if any vs weapons.
from what i remember from an article, the Block skill was mentioned to be more useful and have perks for elemental resistance and/or blocking spells
not too sure though when or where i saw it so dont take my word for sure
but ya, back on the subject of the thread, ya ill be using the magic/shield combo and maybe switch with a sword every now and then