Today Microsoft made Windows 7 (English) available for download for MSDN and TechNet subscribers. Windows 7 will be available for general consumers October 22nd. A complete list of the different availability dates for all type of customers can be found at the Windows 7 blog.
Windows 7 include many new features like touch, Windows XP Mode, support for virtual hard disks (bootable), improved UAC user experience, enhanced Remote Desktop Protocol (RDP) to mention a few.
Scott Hanselman advice developers running Visual Studio 2010 Beta 1 to uninstall Visual Studio before upgrading to Windows 7:
Beta 1 of .NET 4 doesn't survive an upgrade to Windows 7 and leaves the .NET Framework in a goofy and unfixable state. Beta 2 won't have this problem.
Windows 7 can be upgraded from Vista and Windows 7 RC1. It's also possible to upgrade from Windows 7 Beta 1, but not recommended by Microsoft.