So if you have 4 machines running 100gh, then wheater your multiplying or dividing it's done per 100 / machine and not the combined total off 400 ?
If fthat's the ase, then one would need a worker for each of the 4 machines.
General advice, set your minimum difficulty to your hashrate in GH/s divided by 1.4. Some info on difficulty and work submits per minute:
https://bitcointalk.org/index.php?topic=27062.msg3142713#msg3142713Someone else might advice you to multiply by 1.4 or divide by 1.8 or whatever. There is no magic difficulty that you have to use. And contrary to popular belief there is no "sweet spot" difficulty that makes your mining most profitable. Worker difficulty is a trade-off between variance and bandwidth usage (and server load for Bitminter). Follow the link above and read that, especially Organofcorti's analysis, and you'll learn how it works.
Doc, have you considered adding pps?
No time right now. Just trying to keep things running smooth at the moment.