Optimize Guest Performance

With Virtualbox 4.3.13, 3D support is broken for Ubuntu Guests. This is an issue because recent versions make heavy use of 3D. 

One solution is to install the guest additions from the ubuntu repo;

Note: As of July 7, this trick no longer works. The x11 additions (I assume) have been updated to the current (broken) version and no previous versions are available.

sudo apt-get install virtualbox-guest-x11

After doing that and rebooting,  you'll have a guest additions that is one version behind, but it will give you decent video. I stumbled on this solution by accident of course, after trying all the things I listed below. 

/usr/lib/nux/unity_support_test -p

Not software rendered:    yes
Not blacklisted:          yes
GLX fbconfig:             yes
GLX texture from pixmap:  yes
GL npot or rect textures: yes
GL vertex program:        yes
GL fragment program:      yes
GL vertex buffer object:  yes
GL framebuffer object:    yes
GL version is 1.4+:       yes

Unity 3D supported:       yes

Other things to try:

Previously, you could enable 3D acceleration via the following steps:

However, you can no longer do that - but it will be patched in the future

In the interim, you can manage some of the visual affects:

sudo apt-get install compizconfig-settings-manager

sudo apt-get install unity-tweak-tool

And you can remove all the 'scopes and lenses' that fill up your Unity menus

gsettings set com.canonical.Unity.Lenses disabled-scopes "['more_suggestions-amazon.scope', 'more_suggestions-u1ms.scope', 'more_suggestions-populartracks.scope', 'music-musicstore.scope', 'more_suggestions-ebay.scope', 'more_suggestions-ubuntushop.scope', 'more_suggestions-skimlinks.scope']"

Or fall back to an older window manager, such as gnome-session-flashback