Q: What is share difficulty, and what should I use?
Share difficulty is the size of the portion of the current block that the pool hands to your miner to be solved. Over long time periods, share difficulty does not matter, and the default of 64 will work fine for anyone. However, if you experience inconsistent payouts over shorter time periods you may want to set the share difficulty lower on your slower miners. I suggest the following per worker:
Scrypt coins:
250KH and below: 16
250+: 32
500+: 64
1000+: 128
2000+: 256
3000+: 384
4000+: 512