Canonical has a very dedicated team building the Mir display server and they are updating it on a constant basis. The version 0.0.7 has just been released.
Ubuntu 13.10 will have the Mir display server as a default boot option, but until then a lot of work and time will have to be invested in this technology.
Highlights of Mir Display Server 0.0.7:
• Instructions on how to compile Mesa and X.Org with Mir support have been added; • Memory allocations have been reduced by pre-allocating and reusing buffers; • Documentation has been added to the XMir drivers; • The google mock has been removed from the internal source tree.
A complete list of improvements can be found in the official changelog.
Download the Mir Display Server 0.0.7 right now from Softpedia. Remember that this is a development version and it should NOT be installed on production machines. It is intended for testing purposes only.