As stated in patch notes...
Legerdemain now influences the quality of loot obtained from Justice activities.
Higher skill ranks in Legerdemain provide a better chance to "find" higher quality items.
Having run around on a few different characters, at various levels and one with the skill maxed, I'm not only not seeing a difference, but the drops seem to be even fewer. It was actually better before the patch, to where I even found a couple motif books. Now, no matter the skill level, I'm finding quite a few containers/cupboards with nothing but pure junk or totally empty. Did something go wrong?
"Such is the nature of evil. Out there in the vast ignorance of the world, it festers and spreads. A shadow that grows in the dark. A sleepless malice as black as the oncoming wall of night. So it ever was, so will it always be. In time all foul things come forth." -Thranduil