mesa-utils is required for the GNOME System Settings 'Details' panel (formerly 'System Info') to display info about the computer's graphics card driver. Otherwise a rather unhelpful "Unknown" is displayed. mesa-utils was actually in main already (as part of the mesa source package) until Maverick when it was split off as a separate tarball (mesa-demos) that gets released at the same time and by the same people as the main mesa package.
$ apt-cache show mesa-utils
Maintainer: Ubuntu X-SWAT <email address hidden>
Replaces: xbase-clients (<< 6.8.2-38)
Depends: libc6 (>= 2.4), libgl1-mesa-glx | libgl1, libx11-6
Description-en: Miscellaneous Mesa GL utilities
This package provides several basic GL utilities built by Mesa, including
glxinfo and glxgears.
DistroRelease: Ubuntu 12.04
Package: mesa-utils 8.0.1+git20110129+d8f7d6b-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-8.14-generic 3.2.0
Uname: Linux 3.2.0-8-generic x86_64
Date: Wed Jan 11 03:16:40 2012
UpgradeStatus: No upgrade log present (probably fresh install)