Penance is a bit of a problem in low level PUG's.
Its such a surefire fast heal that the lack of threat tools that the Tanks posess at my level, you can be sure that a Fade is quickly incoming from myself.
However, on a Paladin tank it seems to work better.
Once again though its a level relative thing with me and im sure as the levels go up and the tanks tank better, i will be able to use it more.
However, as a levelling tool its brilliant and kicks the living daylights out of mobs whilst using it as an offensive tool.