If you didn't read the latest news about IntelliJ IDEA being released as open-source version, please read the official announcement.
The first Maia Ultimate Edition EAP brings some bugfixes as well as some smaller improvements.
Also support for Convention plugin is starting (little by little...):
The full changelist is available from here.
PS: You also might want to have a look at the revamped Features/Userguide - now with more screenshots.