VirtualBox reached version 3.0.0 recently and seeks to replace such virtual machine programs as Virtual PC, VMWare, QEMU, BOCHS, Parallels, etc. You might remember a project named Xen that was targeted for Linux and other Unix like operating systems. Red Hat added Xen support in their kernel and other Linux companies followed suit. Well now they have VirtualBox support via a kernel mod.
Why should you care that another virtualzation program has hit the market? Freedom of choice, and support from Sun are good answers to that. VMWare Workstation costs money and the free VMWare Server has issues running on certain operating systems. VirtualBox seems to be working better than VMWare in my tests under Linux, and I don't think VMWare supports USB devices or 3D video support yet, at least I couldn't get those when I tried it out in the 6.0 release. But VirtualBox may or may not be right for you. You might be happier using VMWare, Virtual PC, QEMU, BOCHS, Parallels, etc if you are comfortable with them and don't want to switch to a new product.
Sure Sun owns the product, but they also own OpenOffice.Org, StarOffice, Glassfish, Netbeans, MySQL, OpenSolaris, and Java. At least this way you can have support for other Sun products and see how they work together. Sun isn't Microsoft, but they are not Apple or Amiga either.
While VirtualBox does not support as many guest operating systems as VMWare it supports the major ones. BeOS doesn't work, unless you are willing to copy over a hard drive image, but HaikuOS does. OS/2 only works for a certain type. Windows 98 works but has no addons. Windows NT, Windows 2000, Windows XP, Windows Vista, and Windows 7.0 works. Most of the Linux and OpenSolaris systems work. Of the BSD Unix only OpenBSD works, but has no addons.
VirtualBox runs as a host on Windows XP and up, most Linux (with the 2.6 kernel, 2.4 is not supported) and Solaris systems, Intel Mac OSX, but no BSD Unix systems yet.
VirtualBox supports the VRDP remote access service via the display properties, so you can run it on a server and let clients connect to a virtual machine remotely through a VRDP client.
When Windows 7.0 comes out, I heard that the XP Virtual Machine has compatibility issues already and is only available for Windows 7.0 Pro and Business and up, not the Home versions. So I'd recommend the VirtualBox running a copy of Windows XP Pro instead.
Keep in mind that VirtualBox is still new technology and they will support more host and guest operating systems in the future. Some day there may be a BSD Unix hosted version, some day it might support BeOS as a guest operating system as well as the BSD Unix operating systems as a guest OS. If you need those for now, stick with VMWare Workstation if you can afford a license.
VirtualBox supports 3D video display, however, it is turned off by default. You can turn it on with the display properties via a check box. The open source OSE version of VirtualBox does not support USB devices, however, you can get around that by mounting the USB device in Windows or Linux and then adding it in as a shared drive, but you won't get USB access or a USB port in VirtualBox OSE edition, you'll need the commercial version for that to synch up to USB devices, but Sun allows the commercial version to be downloaded for free, but without the source code.
Fedora Forums has a thread with instructions on how to get VirtualBox to work with Fedora 10 and it also works on Fedora 11. You just need to install a kernel mod to get it working.
Using Fedora 11 as a guest operating system under Windows XP Pro caused it to freeze when I did a Software Update. I was able to work out the problem by turning on PAE and Nested Paging options and installing the VirtualBox addons for Linux. The problem went away after that. Reading the VirtualBox documentation and Fedora Forums helped me resolve that.
It is a good virtual machine for supported operating systems, but could be better. I'd like to see VirtualBox support the BSD Unix operating systems, BeOS, AROS, and even Mac OSX under Mac OSX to run older versions of OSX in a VirtualBox. Some guest operating systems need tweaks to the virtual machines settings in order to work properly.