I'd like to see how some classes are implemented in Mono and would like to use code navigation features found in Visual Studio. Has anyone tried importing Mono source codes as a VS project / solution?
Yep, it is fairly simple. The solution file for Visual Studio 2008 is shipped with a source tarball and is located under the *..\mono-2.6.1.tar\mono-2.6.1\mono-2.6.1\msvc* directory (you should specify your mono version of course). Here is a quotation from a readme file:
BUILDING
From this directory type:
msbuild.exe mono.sln /p:Configuration=Debug_eglib
msbuild must be in your path, it comes with the .NET Framework.
Latest sources can be downloaded from here.
EDIT
First of all, mono class library is part of a mono runtime and is being build simultaneously with a runtime. Not all parts of mono (as well as not all parts of a base class library) are written in c#. For example, zlib related stuff is written in C. Building mono is not an easy process, my answer above is just a tip as to where the solution file is located. The complete tutorial on building mono on Windows cold be found here. If you just want to browse a source code, *..\mono-2.6.1.tar\mono-2.6.1\mono-2.6.1\mcs\class\corlib\System* would be a good starting point.