How good a "take off" on the block chain is Factom? An advertisement for Factom says that it improves on "speed, cost, and bloat." And it apparently provides a decent "proof of existence" for people who want to "copyright" their work.

What is it that Factom can and cannot do, especially with reference with the original block chain? Put another way, what are its advantages and disadvantages?
Factom provides a general purpose data layer secured by the Bitcoin blockchain.

Factom is a protocol run by a set of Federated Servers that allow users and applications to create their own "chains" of entries, which are really just whatever data the users and applications wish to track.   

Factom then secures those chains by hashing them together with all the other data from other users, and a single hash is written to the Bitcoin Blockchain every 10 minutes.  Once data is entered into Factom, it cannot be changed, modified, reordered, or deleted.

One way to look at Factom is that it allows applications and users to create whatever data structures they need, then secure those structures with the blockchain.   So Factom provides a way to create audit trails that cannot be modified in any way.  Or ways of insuring entries in databases are both 1) secure, and 2) entered on a certain date.   Ways of creating audit trails for traditional banking that are as transparent and unalterable, and secure as the blockchain.

Because the history cannot be modified, Factom provides some interesting security features.  Identities can be verified and validated, and secured by time; nobody can insert a fake identity into the past.

The use cases are many, and go far beyond copyright.