It's been confirmed now that Qaddafi's troops are using cluster bombs in Mistrata, a city that has been under siege for about a month. According to the Human Rights Watch report: "The cluster munition is a Spanish-produced MAT-120 120mm mortar projectile, which opens in mid-air and releases 21 submunitions over a wide area. Upon exploding on contact with an object, each submunition disintegrates into high-velocity fragments to attack people and releases a slug of molten metal to penetrate armored vehicles."
Cluster bombs are of course extremely controversial--a majority of nations banned the use of cluster munitions through the Convention on Cluster Munitions, which became binding international law in August 2010. Qaddafi's troops are targeting residential neighborhoods with this weapon.
One of the most searing reports out of Misrata is this one, from ITV. Warning: it is graphic.