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

What does the last line mean?
I thought this is a drag-drop file copy feature like VMWare.
I tried that. But I couldn't copy by drag-drop, ctrl-c ctrl-v either.

Edit:
I mean VBox 4.0 beta, not 3.x
The release note is here.
Download link is here.