Sorry if I should not post here for PSI (A separate news group for the semi-open api would be best than wiki notification IMHO if you do not want to use the Open Api forum.)
I have 2 little comments:
1) Consider moving PsiFile.findImportReferenceTo(PsiClass) to PsiJavaFle. Rational: what does it return when it isn't a java file? Should it be valid at all? It doesn't look like it is very cohesive right now.
2) PsiManager.getRootDirectories(int) should be deprecated in favor to a more explicit interface like PsiManager.getRootDirectories(PsiRootPackageType)