Next thought. Can everyone please stop referring to WU in terms of MH/s. WU is not measured in MH/s, it's measured in shares/min.
WU/min and MH/s are the exact same thing, just slightly different units.
For Scrypt 1 WU = 655536 hashes. 1 WU/min = 1.09 kH/s (Different numbers are used in SHA-256)
Cgminer averages the WU and MH/s numbers differently, so they don't quite line up exactly on the display - but they are the exact same thing.
Share difficulty does not affect the WU number. However, share difficulty is measured in WU. So a share with 1024 difficulty needs on average 67,108,864 hashes to solve.