Just a quick note on this – a customer had a question about the old RC4 40-bit encryption yesterday, and this prodded me into taking some memory dumps of intermediate steps and figuring out where my own example code wasn't working. Fortunately, it wasn't really a problem with the documentation – I'd just made a dumb mistake where I put '5' in a loop instead of '16'. I also had a bug in the ManagedRC4 project, so if you already have that, pick up the new one, too.
At any rate, there are now working examples for all of the currently shipping encryption techniques specified in MS-OFFCRYPTO.
Maybe next we can work on getting code up to do signatures, though I think the xmldsig stuff is fairly well covered by the .NET framework already.
The project is at http://www.codeplex.com/offcrypto