IGN discusses the Starcraft 2 units and description. Pretty handy info. Example:

Mothership:
Mothership: Only one of these can be present on the battlefield at a time. They have three powerful abilities, the first of which is called Time Bomb. Unleashing this attack surrounds the ship in a translucent spherical field capable of stopping incoming missiles. When the field times out, the missiles drop to the ground like harmless Tic-Tacs. The second ability, called Planet Cracker, fires a battery of laser beams (the Protoss like lasers, apparently) at the ground, quickly wiping out whatever’s lurking underneath the ship. This ability is particularly useful because the mothership can be ordered around while the Cracker fires, acting like a tornado through a trailer park. The final ability is Black Hole, which, as you might expect, tears a hole in the fabric of “insert nerdy science-fiction term” and actually sucks in whatever units surround it. In the demonstration we saw Blizzard trigger a black hole around about four Terran Battle Cruisers, wiping them out within a few seconds.