It applies to all spells, so it's basically a conditional Quicken that applies only when you make attacks. The Duskblade ability has the advantage that you can use your touch spells multiple times in a full attack, but is limited by Duskblade's small spell list. I didn't want to copy that here mostly because that can get very broken very fast if you start applying better spells to your full attacks, like Poison or Shivering Touch.