From Softpedia...

VirtualBox 3.1.0 Final Released

Oddly, VirtualBox 3.0.12 running under Windows said it is the current release when I selected "check for updates". However, the 3.1.0 update for all platforms is available at...

VirtualBox 3.1.0 downloads page

The Softpedia article mentions several interesting enhancements available in the 3.1.0 release:

- Teleportation: Live VM migration session (wow)
- Network attachment can be changed on a running VM
- Enhanced virtualization performance improvements if hardware assist is available (Intel VT-x or AMD-V)

Addenda:
1. The process of updating from 3.0.12 to 3.1.0 failed on the first try. I ended up terminating the process from the Windows Task manager
2. After rebooting Windows, I made a second update attempt. This time everything proceeded as expected. However, the update process was orders of magnitude slower than previous updates. It took many many minutes for the process to complete
3. I saw an odd MSI installation failure message at the end of the 2nd update attempt. However, VirtualBox seems to run ok and reports that it is version 3.1.0