I am loving Oracle now owning Sun and therefore VirtualBox - or "Oracle VM VirtualBox" as it is now called.
Since it came under Oracle's wing, there have been hundreds of bugs fixed and now the latest release of VirtualBox supports shared disk. Lack of shared disk support has been a complaint for folk wanting to install clusterware of some sort for Oracle RAC installations on VirtualBox.
From the Changelog for VirtualBox 3.2.8:
The following items were fixed and/or added: ... Sharing disks: support for attaching one disk to several VMs without external tools and tricks (see here for a short explanation)