Kerem Kusmezer has sent me an e-mail pointing me to the immediate availability of the .NET Mass Downloader 1.1. According to the CodePlex project page

[...] While it’s great that Microsoft has released the .NET Reference Source Code, you can only get it one file at a time while you’re debugging. If you’d like to batch download it for reading or to populate the cache, you’d have to write a program that instantiated and called each method in the Framework Class Library. Fortunately, .NET Mass Downloader comes to the rescue!

Unfortunately I could not yet give it a test drive as CodePlex constantly reports "Server too busy!". I'll come back to it later.