Q: If a duskblade scores a critical hit when channeling a spell through a melee attack, is the spell’s damage multiplied just like the weapon’s?
A: The rules aren’t as clear as they could be, but the Sage is inclined to say no. Here’s the key sentence, from the PHB II, page 20: “If the attack is successful, the attack deals damage normally; then the effect of the spell is resolved.” If you score a critical hit, the attack deals the normal (critical) damage. Then the spell resolves normally, but it’s just a rider effect applied due to the successful attack roll—you’re
not actually using the spell in the normal manner, so it can’t score a critical hit.