Anyone running Ubuntu as a Virtualbox guest is advised to update to Virtualbox 4.0.6 (+ the extensions) that was released today. Don’t forget to recompile the guest additions after upgrading to 4.0.6. Besides the usual stuff in the changelog, the update fixes a problem with screen resolution in Ubuntu 11.04. Since the Ubuntu update is just around the corner updating Virtualbox beforehand will prevent a bit of hassle.