Pythonid, the plugin providing support of the Python language in IntelliJ IDEA, has finally been released. You can download it from the IntelliJ IDEA Plugin Manager (Settings | Plugins), or from the plugin repository.
The plugin is currently compatible only with IDEA 5.1.x. Demetra compatibility will be provided in the next build of Demetra.
Pythonid was developed by me and Keith Lea. This is not an official JetBrains product; I work on the plugin only in my spare time. The plugin is open-source, and the source code is available at http://pythonid.dev.java.net. People willing to contribute to the plugin development are very much welcome; if you're interested, please contact me to discuss the details.