[vermaden]

http://forums.virtualbox.org/viewtopic.php?f=15&t=36748

Version 4.0.0 will be new major release. The following major new features were added:

New settings/disk file layout for VM portability; see the manual for more information.
Open Virtualization Format Archive (OVA) support; see the manual for more information.
VMM: support more than 1.5/2 GB guest RAM on 32-bit hosts
Language bindings: uniform Java bindings for both local (COM/XPCOM) and remote (SOAP) invocation APIs
Chipset: added support for the Intel ICH9 chipset with 3 PCI buses, PCI express and Message Signaled Interrupts (MSI)
Audio: Intel HD Audio is now available as guest hardware, for better support with modern guest operating systems (e.g. 64-bit Windows; bug #2785).
GUI: redesigned user interface with guest window preview
GUI: new display mode with downscaled guest display
Resource control: added support for limiting a VM's CPU time and IO bandwidth.
Storage: support asynchronous I/O for iSCSI, VMDK, VHD and Parallels images
Storage: support for resizing VDI and VHD images
Windows Additions: support for automatically updating the Guest Additions (requires installed Windows Guest Additions 4.0 or later)
Guest Additions: support for copying files into the guest file system