Visual Studio 2012 and .NET 4.5 are ready to go
infoq.com
infoq.com
Wow, 50 million lines of code is completely earth shattering to a student like myself who has only dealt with line counts that were five digits long.
I don't have any specific knowledge about VS, but most giant software projects (including Eclipse) with LOC counts in the millions don't exist as singular projects - rather, they are made up of lots of smaller, loosely coupled projects with generally well-defined integration points.
It certainly isn't easy - defining those APIs in a way that their surface area is the correct size is insanely difficult - but it does make managing projects of this size at least manageable.