burnside, add the ability to reduce difficulty for a certain worker so that shares are found easier.
why
A number of pools implement variable-difficulty shares so that any given worker is submitting at a roughly constant rate whether it's a CPU-mining Raspberry Pi or an overclocked 6-GPU monster. It helps the pool by preventing it from being share-spammed into oblivion by large rigs, and helps the miner by giving relatively stable error bounds on share submission.