Just saw that the much anticipated Oracle Data Modeling tool is available for download here:
Once you fill out a quick survey, you can download a complete build with JDK, or just the build for your specific OS.
I have the Mac OS version up and running, and will be putting it to work today on a number of different projects. I'm glad to see that an enterprise-level data modeling tool has finally come to Mac OS X. One more item on the list can be checked off!