I have Slackware 13.37 x64 installed as guest OS on VirtualBox 4.1.2. Gueast Addition are installed. Everything works fine inside Slackware. It uses my secondary monitor in fullscreen mode. [Just tested, everything works fine in seamless mode]
My mouse is a Microsoft Wireless Mouse 5000 and I have the latest version of Intellipoint software. Button settings (in picture) stop working while the virtual machine is active. The mouse acts as if Intellipoint is not even installed. Restarting Intellipoint doesn't help.
For reference, my machine is a Core2Duo with 6 GiB of RAM; OS is Windows Server 2008 R2.