We are fortunate that IAC numbers are unique across members. This lets us tell one "John Smith" from another, and makes member lookups relatively easy within our scripts.
We sometimes want to create non-member accounts for test purposes, or as a courtesy to friends of the IAC. We assign those accounts fake IAC numbers in the form 9999xxxx, so that various bits of code can exempt them from our standard business rules (e.g. expiration dates) as appropriate.
I've developed a report, www.iac.org/special-accounts, that displays these non-member users.
