Note: I did not uninstall IntelliJ 11, yet.
Next, run sbt and on the sbt console, run update and then gen-idea
Every time I opened IntelliJ 12 it would pop up a few annoying notifications about the fact that I had not configured Android development plugins.
So, I uninstalled IntelliJ 12 and chose not to import settings.
Now, the problem was that none of my Scala source files had Scala syntax coloring. Then, I got a popup griping about the fact that the Scala facets were not installed/configured.
So, I got the IDEA Scala Plugin for IntelliJ 12 (see URL below), went to IntelliJ Preferences | Plugins and clicked the "Install plugin from disk..." button.
Preferences ModificationsChange the color theme in IntelliJ Preferences | Appearance to the new Darcula theme
Change Tab Size (and Indent) to 2 spaces in Code Style | General
Check Editor | Appearance "Show line numbers"
Get IntelliJ 12 here: http://www.jetbrains.com/idea/download/
Get latest Scala Plugin for IntelliJ here: http://confluence.jetbrains.net/display/SCA/Scala+Plugin+Nightly+Builds+for+Leda