Eric Lippert has posted Eric's Complete Guide to BSTR Semantics. This is a document that is widely valued within Microsoft, since BSTR semantics are rather tricky, and I'm glad he's willing to share it with the world.

In particular, Eric spends quite a bit of time discussion the very important equivalence of NULL and L"" in BSTR semantics, something that is buried in paragraph seven of an MSDN document you probably didn't even bother reading.

If you ask nicely, you might be able to convince him to post his "Complete history of OLEDATE".