New dates for Visual Studio 2010 and .NET Framework 4 RTM are announced today. The official RTM date is 12th April 2010. As I wrote before, in February there will be released also Release Candidate version.
Microsoft will be supporting upgrade from Beta 2 to RC, Beta 2 to RTM and RC to RTM so there is no reason why you should not upgrade today or at least start planning it. A full TFS upgrade can take a lot of time so you better plan it. I will write a follow up post on common pitfalls during TFS 2008 to TFS 2010 upgrade process.
If you have any problems upgrading TFS 2008/2005 to TFS 2010, please feel free to contact me.