Microsoft has listened to user feedback concerning Visual Studio 2010 Beta 2 performance issues and bugs and decided to extend the Beta period. The new Visual Studio version introduces numerous changes, including many that focus on multicore programming. A new checkpoint release, a Release Candidate would be publicly available during February 2010.
S. Somasegar, Senior Vice President, Microsoft Developer Division made it very clear in his blog post "Visual Studio 2010 and .NET Framework 4 Beta period extended". The launch of Visual Studio 2010 and .NET Framework 4 won't be in March, it would a few weeks later than expected in order to react to the new feedback obtained with the forthcoming Release Candidate.
For more on this topic, see Gaston Hillar's report here.