Key features of Oracle VirtualBox 4.2 include increased efficiency, VM Groups support, more flexible VM startup options, networking improvements, and new platform support (Oracle Linux 6.3 and Windows 8 and Mac OS X 10.8).
Aside from those features pushed in the Oracle press release, there's other improvements too. some of the finer details include user-interface improvements, support for up to 36 network adapters, support for limiting network I/O bandwidth to VM guests, experimental support for drag 'n' drop from the host to Linux guests, improved VM context switching performance for Intel CPUs, improved AMD Bulldozer support, and much more.
VirtualBox 4.2 is available for download from VirtualBox.org. The VirtualBox 4.2 virtualization software succeeds VirtualBox 4.1, which is now more than one year old with its gold release happening in July of 2011.
From last month I do have early VirtualBox 4.2 benchmarks but more Oracle virtualization tests are on the way. Also see VMware Virtualization With OpenGL Still Smacks Oracle VirtualBox and VMware Fusion Stuns VirtualBox In CPU Tests.