Well, I work on a large healthcare administration system, and we use inheritance a fair bit (both "real" inheritance via @ISA or use base as well as "fake" inheritance that is done manually, or via code attached to hierarchical data-structures of some form or another). A typical example is something like (BCBS is lingo for "Blue Cross and Blue Shield" and MA is Massachussets):

"A BCBS-MA HMO Blue claim ISA BCBS-MA claim ISA BCBS claim ISA claim."

Details get complicated and uninteresting from there, and that isn't quite an *exactly* correct example, but it gets the idea accross.

There are business rules that apply specifically to BCBS-MA HMO Blue that make it behave differently than, say, BCBS-MA PPO. There are business rules that apply to all BCBS-MA plans that aren't common to other state/region BCBS's. There's also general stuff that all BCBS's have in common, but which are different when compared to large comercial insurance carriers like Aetna and Cigna, and likewise different from government carriers like Medicare, Medicaid and Champus (veterans). However, there are some things that are really the same between all of these.