OrderBy and OrderByDescending are stable?

Yes, they're definitely stable. I picked up the same error in my review of the book.

Joe responded to that bit of my review with this:

Just for your reader's knowledge, the ordering is now specified to be stable. Initially it was unstable, and was later changed to be stable but I was told it would be specified to be unstable, but apparently at some point, the specification was changed to be stable. My book was updated but apparently I missed a spot.

So yes, it was a mistake.

Overall it's a reasonably accurate book. (There are a few inaccuracies which are due to MSDN being inaccurate, but that's fairly easy to forgive.) There are far worse around :)

According to MSDN, OrderBy is stable, as is OrderByDescending.