Systems that need to:

- prove a process
- prove existence of something (historical fact checks for example)
- prove the record exists (for auditing, but different than above)

I could see this being useful as an intermediate hash table sitting inbetween a front end web application, and a BPO system http://en.wikipedia.org/wiki/Business_process_outsourcing

In terms of consumer oriented use cases, I think the appeal would be privacy as some transactions may not want to be broadcasted on the Bitcoin Blockchain - the ability for Factom to encode transactions offchain would mean that this can act like a dark pool