Note: As of version 4.0, VirtualBox introduces the Extension Pack mechanism which allows Oracle and 3rd parties to deliver additional functionality on top of the standard Open Source product. The Oracle VM VirtualBox Extension Pack, adds support for USB 2.0, RDP server and the PXE bootloader with E1000 support.
You can download this Pack from the same location and install it via the VirtualBox Global Settings using the Extensions pane.

This is the third beta of the upcoming 4.0 release. The following items were added/fixed since VirtualBox 4.0.0 Beta 3:

• Audio: fixed memory corruption under certain circumstances
  
• 3D support: fixed OpenGL support for Windows 2000 guests
  
• Settings: modifying VM session could lose disk attachments (4.0 Beta 3 regression)
  
• OVA: fixed crash during import
  
• GUI: better OS type string matching
  
• GUI: fixed redraw problem on X11 guests with multiple monitors attached (Mac OS X hosts only)
  
• GUI: remember last directory in file dialogs
  
• Settings: fixed .vbox file format portability issue with snapshots (backslashes)
  
• ExtPacks: fixed installation on certain Linux hosts (e.g. openSUSE)
  
• ExtPacks: require sudo for installation on Linux and Solaris hosts
  
• Storage: fixed possible crash during suspend
  
• Storage: fixed raw disk access on OS X
  
• Storage: lower the CPU usage for low disk I/O bandwidth limits
  
• Storage: added multi-attachment image mode for shared disk clusters
  
• Storage: fixed SATA activity LED handling
  
• 2D: fixed seamless mode when 2D is on for Mac hosts
  
• Additions: fixed incompatibility with SLED 11

VirtualBox 4.0.0 Beta 4 Known Issues:

• Host-Only Networking as 2nd adapter, no IP address assigned
  
• 3D Acceleration: VM Crash on NVIDIA
  
• GUI crashes (OpenSuse Host)
  
• Linux guest: Xorg segfaults
  
• Seamless mode and multi-monitor
  
• [Hard to Reproduce] Portability: VMs could not find image
  
• Portability: Shared folder path is not absolute
  
• Regressions: Linux Additions several failures
  
• [Hard to Reproduce] VM doesn´t start after shutdown
  
• [Hard to Reproduce] GUI: Can´t Uninstall ExtPack
  
• Portability: Live Snapshots cannot start
  
• VMM/Guest SMP: Very slow performance on over-commit
  
• [Hard to Reproduce] Can´t uninstall BETA3, upg to BETA4 fails