1. It's true that the reference source site has been down for several days but now appears to be up again
2. It's also true that NOBODY from MS has been responding to questions about the lack of .Net 4.0 source code, or any other question for that matter about reference source
I'm not bashing MS in general; in fact, I make my living by developing solutions centered around MS technology. However, I'm extremely annoyed at the lack of proper maintenance of the reference source archive. Not only about the bits that have never made it there to begin with, but that almost a month after the release of .Net 4.0/VS 2010, there's still no code for .Net 4.0. !
The lack of of .Net 4.0 code bugs me too. But fortunately VS 2010 supports .Net 3.5 too, so its easy to figure out the issue by debugging using 3.5
When the reference site was down even that was possible.
Unless you are using the new concurrent stuff or other .Net 4.0 specific stuff, debugging in 3.5 works fine.
I used to clean the my symbols cache folder periodically., but I have figured out how valuable it can be when Microsoft site goes down.