The duskblade's special ability arcane channeling is supposed to make the duskblade's full attack awesome. When the special ability says that "the spell affects each target you hit in melee combat that round" (PH2 20) that can totally be the same target multiple times.
Touch Spells versus Spells Requiring Ranged and Melee Touch Attacks
I suspect that there's some confusion between spells that require a melee or ranged touch attack to function and the touch spell described in the duskblade's special ability arcane channeling (i.e. "[Y]ou can use a standard action to cast any touch spell you know and deliver the spell through your weapon with a melee attack," and, "[Y]ou can cast any touch spell you know as part of a full attack action, and the spell affects each target you hit in melee combat that round").
These two kinds of spells are not the same thing.
A touch spell is a spell with a range entry of Range: Touch. Spells with a range that isn't touch can't be used with the special ability arcane channeling. For example, the 1st-level duskblade spell chill touch [necro] (PH 209) is a touch spell, while the 2nd-level duskblade spell scorching ray [evoc] (PH 274) is not a touch spell, having as it does a range entry of Range: Close, even while requiring a successful ranged touch attack to inflict damage.
The duskblade's special ability arcane channeling is quite powerful when combined with a touch spell that is usually discharged after but a single successful attack (e.g. the 2nd-level Sor/Wiz spell combust [evoc] (SpC 50), the 9th-level Sor/Wiz spell imprisonment1 [abjur] (PH 244)), allowing several high-powered effects as a single full-round action.
- Hey, a gestalt duskblade // wizard could do it.