A few things...
The Duskblade's arcane channeling abilty at 13th level specifies the spell is discharged at the end of the round, regardless of the duration of the spell. This also applies to the # of touches allowed by, for example, the "Chill Touch" spell (BTW, i think this is the only spell in the Duskblade's list, to which this rule applies). This also means that the spell is still applicable for AoOs occurring until the end of the round.
Strangelly, and assuming your DM allows you to deliver several touches with a channelled "Chill Touch", this means that if you miss with the first attack (in which you channelled the spell), you can perform a full-attack in the next round, delivering an alloted touch of the spell with each hit. This makes it superior to the 13th level ability, yes, but again, i think this is the only spell to which this applies.
IIRC, the damage from a spell delivered by arcane channelling is considered as a ride-on effect and, as such, "extra damage", so:
- you can't score a critical with a channelled spell
- it's roughly equivalent to SA damage for other purposes
Yes, you can SA with a spell, but only spells that need an attack to deliver can be used for SA. When channelled, the spell becomes a ride-on effect (like the extra fire damage from a flaming weapon), so the SA damage is dealt with the weapon, not the spell.
