Sandcastle has been an interest project for M$. With the demised of the OSS project "NDoc" (due to lack of support), its successor "SandCastle" made a worthy replacement.
There were some issues with it... in true M$ style it wasnt the easiest to just pick up and use, but in saying that it was kind of a 2this is what we use if you want to use it here you go" no warranties etc...
The next part of the saga was M$ putting sandcastle on CodePlex which is the OSS portal for M$ tecnologies, and IMO a great advancement for M$ to start working more closely with its community. Unfortunately Sandastle was not open source and the source was never posted, which kinda defeated the purpose of it being on code plex... I have a feeling it was only there as there was no where else to put it.
The inevitable happened and it was pulled form the site... which sucks... it effective meant there was now no widely used and accessible code documenting software for .net code.
Thankfully an "outcry" occured, 'twas a small one but loud enough for those that needed to hear. So it looks like instead of taking it away M$ have now release the actual source so it can be on codeplex with out the associate compliants and bagged that would come with a closed project being housed there.
I s'pose al is well that ends well.