Hi,
I'm making a design decision about a database that stores contact info (name, address, phone, etc) amongst other things. The contacts are members of one or more of our organization's "networks" (i.e. mailing lists). There's one staff member here in charge of each network.

I need to decide whether each contact should have one owner (i.e. one staff member allowed to edit the contact info), or if I should allow one staff person from each network to modify the contact info (with email notification to other owners), even if this means that an individual contact has several owners. Any suggestions on what works best in practice?

The problem you're presenting is really about business rules. This is a job for an analyst working with the client. The business rules the analyst comes up with are then incorporated into the design.

If you are the one doing the analysis stop designing, pull your clients together present your case and let them provide the answer.

That would be the industry standard approach.