Whenever you read about a new Java ORM tool, one of the big marketing points always seems to be how you can write your objects seperate from the datatabase and just 'map' them.  And if the database changes, you can just keep the objects you have and map them differently.

That is a very bad premise, and responsible for untold long nights of coding.  Well normalized database tables in conjunction with their contraints give a very clear logical understanding as to how the problem domain exists.  Developers should be looking there first in order to start writing their applications.

ORM is a good thing because it simplifies most the hassle involved with using the JDBC API and mapping the contents of the ResultSet object into something that can be worked with.  If you use it to simplify data access, it is of great benefit; however, using it to make two conflicting data models will end up in some very long hours trying to make things just work.