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.
According to our research and experience there shouldn't be any issues with VS 2005, 2008, 2010, 2012 and 2013. I personally tested the changes with VS 2008 and 2010 and 2013 was tested by another team member. In all tested versions, the multi-process build setting worked as expected using all available cores/threads, even in the aged Visual Studio 2008 (with SP1).
As always, if anyone sees any issues 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 with the added /MP flag in usage. CPU is a Quad-Core with Hyperthreading, all threads are used which leads to almost 100% CPU Usage. The CEGUI team stands united in the belief that this screenshot will amaze absolutely everyone.