Microsoft has released the specifications for Visual Basic 9. This implies that the language is hardening and probably will not change much between now and the release date, expected to be later this year.
Specifications are not something Microsoft has traditionally provided in the VB family of languages. Designed more for business and casual users, the documentation normally takes the form of a "programmer's reference", which is more instructional in nature than a reference manual.
In these days of heightened concern over cross-platform support, language specifications are viewed as essential. Projects like Mono would not be possible without the wealth of specifications available for the .NET platform. Languages without specifications such as Ruby are posing a particular problem for people trying to port them, especially when a clean-room implementation is desired.
It should be noted that unlike C# and the API itself, Visual Basic is not a standard itself. While the specification is available, there is much debate on whether or not it can actually be used. This is not a new debate, questions over language ownership and rights have been going on since the dBASE clones first appeared decades ago.
Language specifications don't only benefit compiler writers. Developers of products like ReSharper and Refactor/CodeRush need the detailed parsing information found in the specification, especially as the language grows ever more complex.