Wikipedia's Visual C++ page has a recap, which I imagine will be updated frequently as we get closer to the release:
  Visual C++ 2010 (known also as Visual
  C++ 10.0) is planned for release on
  April 12, 2010. It is currently in
  development, and available publicly
  only in the form of beta version, and
  available on MSDN as a release
  candidate. The Visual C++ team is
  considering using a SQL Server Compact
  database to store information about
  the source code, including
  IntelliSense information, for better
  IntelliSense and code-completion
  support. This version adds a
  modern C++ parallel computing library
  called the Parallel Patterns Library,
  partial support for C++0x,
  significantly improved IntelliSense,
  and performance improvements to both
  the compiler and generated code.
  This version is built around .NET 4.0,
  but supports compiling to machine
  code. The partial C++0x support in
  VC10 consists of 6 compiler features
  (lambdas, rvalue references, auto,
  decltype, static_assert, nullptr), and
  some library features (e.g. moving the
  TR1 components from std::tr1 namespace
  directly to std namespace). Variadic
  templates were also considered, but
  delayed until some future version due
  to lower priority which stemmed from
  the fact that unlike other
  costly-to-implement features in VC10
  (lambda, rvalue references), this one
  would benefit rather the minority of
  library writers than the majority of
  compiler end users.
  
  
  - Beta 2 version number: 16.00.21003.01 (this is the version of compiler; the IDE itself has version number 16.00.21006.01)  
- RC version number: 16.00.30128.01