I've heard many times both in conversation and in blog posts that ObjectBuilder doesn't have any documentation. Granted, yes it doesn't have good (if any) official documentation.
However, the Composite UI Application Block (CAB for short) does have a good bit of documentation on ObjectBuilder in the hands-on-labs (VB version, if you are so inclined). Section 8 will give you a full architectural run down, which to me is far more valuable than class-by-class documentation. After that, the best source of documentation is probably the source code.
Anyone else know of any good documentation for ObjectBuilder, official or otherwise?