I'm a metallurgist, but have never worked with it & am not a 'DU expert' by any stretch. A friend of mine did his post-doc with DU and knows it fairly well.
It is somewhat similar to lead in its properties (easily cast), and is more 'toxic' than lead. Wouldn't want it in ground water sources for instance.
It is not radio-active in the sense that these kooks make it out to be. The radium (glow-in-the-dark) on watch hands is far more 'radio active' than DU ammo.
DU is desireable for ammo, because it undergoes 'adiabatic shear' at high strain-rates. In other words, when it is deformed very quickly (shot from a gun) it becomes progressively sharper, and continues to shear itself into a sharp point during penetration.
Other metals 'behave as liquids' at high strain rates, i.e. bullets 'mushroom' and have limited penetration because of it.
Also--what about Am in smoke detectors...8^)