For all future Releases and all current branches (v0, v0-8, default branch) the /MP option for building multiple processes has now been enabled. This means that CEGUI will build faster if multiple cores/hyperthreading threads are available.
We consider that there shouldn't be any issues with VS 2005, 2008, 2010, 2012 and 2013, which are the only versions we currently support. I personally tested this with VS 2008 and 2010, in both version it worked fine and the build used all my cores, even in the aged Visual Studio 2008 with SP1.
If anyone sees an issue that could arise due to this change, please inform us about it in the forums or by chatting with us in our IRC channel.
Below i added a screenshot from VS 2010 building CEGUI, which shows 100% CPU. The CEGUI team stands united in the belief that this will amaze absolutely everyone.