I am in the B2B space and have some unique requirements arround customers. In the B2B world you have two objects to consider instead of just "customers", typically these objects are referred to as "Accounts" & "Contacts". Where every contact belongs to an account. Ideally you would want the extension to handle a few standard B2B functions.
1) Set a credit limit on the account
2) Save Ship to addresses on the account level
3) Allow the contact to view and use the ship to addresses of the account.
4) Allow a log in for the account or a manager role who can maange the contacts on the account.
I have seen a few extensions that try to resolve this but i'm not quite sure if any are all the way there for a complete B2B account/contact relationship.