I just needed to find an answer to a question in MonoRail. MonoRail code base is over 75,000 lines of code, including all the supporting projects and tests. Castle.MonoRail.Framework has about 37,700 lines of code. The question was something that I never really thought about, and had no idea where to start looking at. I opened the solution and started hunting. It took about five or six minutes to find the correct spot, another two to verify my assumption and be shocked that there is a private method there :-) and then I was done.
Under ten minutes, to find a question that I never thought about in a significant code base. ReSharper helps, of course, but nothing beats well structured code for maintainability.
Oh, and MonoRail has very little implementation documentation.