In regards to all the usefull skills that can currently be cross classed:

¤ No Sentinel for Monk, Dragoon, Bard or Black Mage
¤ No Second Wind for Paladin or Bard.
¤ No Featherfoot for Paladin or Bard.
¤ No Raise for Monk, Warrior, Dragoon or Blackmage
¤ No Sacred Prism for Monk, Warrior, Dragoon or Blackmage
¤ No Cure/Protect/Stoneskin for Monk, Warrior, Dragoon or Blackmage
¤ No Sanguine Rite for Paladin, Monk, Warrior, Dragoon or White Mage
¤ No Chameleon/Quelling Strike for Paladain, Warrior, or White Mage
¤ No Decoy for Paladain, Warrior, or White Mage
¤ No Invigorate for Paladain, Warrior, Bard, White Mage or Black Mage
¤ No Keen Flurry for Paladain, Warrior, Bard, White Mage or Black Mage

However, I am not sure about all skills of the secondary classes being equippable. On the tooltip, Cura and Curagae require CON. It will be usable by WHM but I am not sure if that limitation means a PLD can't use it.