SQL Developer 3.0 Early Adopter 3 is available for download.
The main new features is the integration with SQL Developer Data Modeler 3.0, providing read and write access for designing and developing data models
(The readme.html for SQL Developer Data Modeler 3.0 can be found in the SQL Developer installation in the folder \sqldeveloper\sqldeveloper\extensions\oracle.datamodeler).
Full new feature list.
update: new EA 4 available
Update: links removed -> final version 3.0 available