It was just on Monday that Oracle released Oracle VM VirtualBox 4.0 Beta 1
with the introduction of "extension packs", OVA format support, ICH9 and Intel HD Audio support for guests, a revamped user-interface in some areas, support for limiting a VM's CPU time and I/O bandwidth, and a number of other changes. Three days later, however, this release has been succeeded by VirtualBox 4.0 Beta 2.
VirtualBox 4.0 Beta 2 doesn't bring any new features, but it does bring a number of fixes, including fixed HDA audio for Ubuntu 10.10 and OpenSolaris guests, DVD detection is working again for Solaris guests, corruption with a-synchronous using the VMDK image, and multi-monitor support on X.Org Server 1.3+ have been resolved, among other work.
The VirtualBox 4.0 Beta 2 release announcement with download links and the complete bug-fix list for this newest version is available from the VirtualBox mailing list