Blizzard still appears to be toying with how active skills are swapped in and out. In Diablo III, you'll eventually unlock six slots to assign active skills and three slots for passive skills. These function as your character build and are easily modified, letting adjust your class' strengths on-the-fly. Initially in the beta it was possible to swap out skills as often as you liked, though Blizzard was concerned this ease of switching encouraged you to play with the skill window open at all times. A later version required you to visit an altar in town to switch skills, locking out your ability to change skills in the field. In the current version of the beta, you can again swap skills whenever you like, though swapping triggers a 30 second cooldown during which swapping is blocked.