Matthias:
It's a little hard to follow what you are doing, but I think the problem may lie with the second relationshipList. Each relationshipList should maintain a single relationship, e.g., Region -> Country or State -> Region.
When you change the Service, you should see both the Company and Contracts reset every time, if I understand how you are calling SPCascadeDropdowns. It might help if you could post your code.
I'm not caching the results because, if you think about it, the amount of data is highly unpredicatable, as is the client machine's capability. In v0.7.2, I'm introducing some rudimentary caching in the core functions to see how people end up using it.
M.
