There had also been various optimization work on rendering traversal code, file i/o and other things.
For v2.4.1, SoExtSelection LASSO and RECTANGLE select could be aborted by the end-user by hiting the 'END' key. No API-changes was needed for this of course.
For v2.4.2, we hacked in support for compressed textures through an API/ABI-invisible field in SoTexture2, called 'enableCompressedTexture'. This field will remain 'invisible' until Coin v3.0.0 is released, and can only be accessed from .iv-file input or through the SoFieldContainer API.
For v2.4.6, SbViewVolume::getAlignRotation() was implemented, and SoToVRML2Action got support for SoUnits in relation to SoVRMLTransform nodes.
New features for Coin v2.3.0 are here.