VirtualBox's limitation of 128MB vram (256MB if you increase it on a VM via the command line) is the worst. The entire rest of the application is pretty much completely worthless without adequate video memory for modern OSes. Install Windows and poof popup saying simple UI is being used because there's not enough video memory... :/
Yeah, I know it supposedly doesn't matter because your video card is doing all the rendering anyway... at least according to the VBox people. Unfortunately Windows and Linux think they only have 256MB of video memory, and it makes VBox useless for many tasks (that have nothing to do with playing games).