“A Graph Database –transforms a–> RDBMS”

The Neo4j site appears to signify whatever that you can do in RDBMS, that you can do in Neo4j.

Before selecting Neo4j like a alternative to have an RDBMS, I want some doubts clarified.

I'm thinking about Neo4j for

  • capability to do rapidly modify data "schema"
  • capability to express organizations naturally rather than relations and normalizations
  • ...which results in highly significant code (much better than ORM)

This can be a NoSQL solution I'm thinking about for it's features, not high end.

Question: Does Neo4j present any problems that could make it unacceptable like a RDBMS alternative?

I'm particularly worried about these:

  • can there be any DB feature I have to implement in application logic? (For instance, you have to implement joins at application layer for any couple of NoSQL DBs)
  • Would be the fields "indexed" to permit a research faster than O(n)?
  • How do you handle hot backup copies and replication?
  • any difficulties with "changing" schema or letting organizations with various versions from the schema living together?