What are examples of Non-deterministic Force.com formula fields in Salesforce?

Reference other entities (i.e., fields accessible through lookup fields
Include other formula fields that span over other entities
Use dynamic date and time functions (e.g., TODAY and NOW)

A formula is also considered non-deterministic when it includes:

Owner, autonumber, divisions, or audit fields (except for CreatedDate and CreatedByID fields
References to fields that Force.com cannot index
Multi-select picklists
Currency fields in a multicurrency organization
Long text area fields
Binary fields (blob, file, or encrypted text)