Microoptimization, util.HashMap is twice faster than mutable.HashMap.
Optimization for local members resolve to avoid treeWalkUp, where it's not necessary.
Making n^2 algorithm for adding members to implicit processor linear
Hashcode for types is lazy now. Probably it's not right solution for conformance cache, but now it's faster.
Cleanup
Improvement for implicit-heavy projects, it's better to analyze implicit functions without explicit return type in the right order.
Cached isAliasType method.
projection.actualElement improved to avoid precedence checking, which is not neccessary.
Don't calculate precedence, when executing Predef and scala package members.
Better check order
ScalaFileImpl: allow to specify a custom file type in the constructor
Extension point: ScalaFileFactory
ScalaFileImpl: allow to customize the set of implicitly imported entities
Implicit search depth default -> 5, to make it more usable in some cases.
Update plugin.xml for the upcoming IDEA 12.1 release
Implicits for Scalaz is twice faster now. Implicit parameters, which require local type inference has less priority over  implicits, which is not require it.
Small improvement for implicit conversions (there is no possibility to use conversion with implicits, where implicit parameters have type parameter in type).
Implicit parameters search performance improvement, don't calculate recursion, until we really need it.
More reflection in ScalaTest support #SCL-5512 Fixed
Monitor "auto-make" and "parallel compilation" settings in Scala projects
Handle compile server startup errors