Now up to a release candidate, VirtualBox 4.2 is past its feature freeze and more stable than the beta but is not yet considered production ready. VirtualBox 4.2 RC1 incorporates fixes in the days since the beta one release.
Among the VirtualBox 4.2 features are improved support for Microsoft Windows 8, GUI improvements, support for up to 36 network interfaces, experimental support for drag-and-drop- from hosts to Linux guests, host parallel port pass-through on Windows, improved VM context switching performance for Intel CPUs with nested paging, AMD Bulldozer improvements, and various other fixes and minor enhancements. There's also support for QED and QCOW images within the VirtualBox Storage mechanism.
The VirtuaBox 4.2 RC1 announcement can be viewed at vbox-announce. At this rate, expect the final VirtualBox 4.2 announcement in the very near future.