While it's not coming down as a stable release update for Ubuntu 13.10 users, Mesa 10.0 is now found inside Ubuntu 14.04 and its latest development state. Information about the recent packaging changes can be found via Launchpad and trusty-changes. For the past several days prior to hitting trusty-proposed, there's been a public call out for testing their PPA, per Ubuntu 14.04 LTS To Land Mesa 10.0 Next Week.
The Mesa 10.0 packaging does include the Ubuntu patches, including the Mir back-end support since it still hasn't been merged into mainline Mesa. Mesa 10.0 upstream offers tons of new features, including OpenGL 3.3 compliance for core Mesa and the Intel Ivy Bridge / Haswell graphics cores.
For all Radeon, Nouveau, and Intel users, using Mesa 10.0 over Mesa 9.x is generally a huge improvement. The next Mesa release should also be out in about three months, so there's also a chance of that hitting Ubuntu 14.04 LTS. Meanwhile, on the kernel side, they are likely using a Linux 3.13 "franken" kernel.
For Ubuntu Linux users wanting Mesa 10.0 but not comfortable upgrading to the Ubuntu 14.04 development series, one of the easiest ways to obtain the newest open-source GPU driver components is by setting up the Oibaf graphics packages.