In my experience it is quite a good idea to install and run a test OS in Virtual Box. But there are some drawbacks you might want to consider:
- All CPU demanding processes will run a bit slower in a virtual machine.
- 3D graphics even though available to some extent is slow and not suited for gaming (but sufficient for Unity).
- Bugs you may experience may not only come from the applications but also from the virtualization environment.
- Updating Virtual Box and the virtual machines installed may take some of your time.
- Some hotkeys of the host (e.g. Super, Ctrl+F.., etc.) do not work without tricks in the guest OS. Likewise some key combinations are reserved by Vitual Box and can not be used in the guest OS.
Still there are advantages that a dual boot solution can not offer:
- Immediate switching between host and virtual OS without needing to reboot.
- Running the test OS parallel to the host OS (depending on your hardware you can even run multiple virtual OSs in parallel).
- Possibility to save snapshots before you do possible harmful things that enable you to restore the previous functioning state if something goes wrong.
- Keep your virtual guest machines over host OS upgrades. You can even carry them to another OS (e.g. Windows, MacOS, other Linux distribution) without any problems.
- Simultaneous file access through networking.
To take full advantages of Virtual Box it is a good idea to run the latest release installable from a repository maintained by Oracle that gives you automatic updates. If you need USB2 or RDP support you also may want to install the Virtual Box Extensions (which makes it a closed source but still free version).
For running Unity, unlimited screen geometry, some 3D graphics support, and Virtual Box shared folder suport we also need to install the Guest Additions.
Let me suggest you try it out with you present 11.10 installation (or in your 12.04 Beta installation). Your virtual machines will not be touched trough an upgrade, just keep them running almost forever (I still have a machine here I built from Ubuntu 9.04).