Here’s the introduction to the release announcement:
This is a relatively small update to bring our free tools release into line with Visual Studio 2010 SP1, announced by Jason Zander here. Visual Studio 2010 SP1 included a relatively small number of fixes to the F# 2.0 Compiler and Library (see the Visual Studio Team description of SP1).
Perhaps more importantly, this release includes the core F# support to enable F# 2.0 development for Silverlight 4 and Silverlight 5 . Once you install Visual Studio 2010 SP1 (and, if using Silverlight 5, the Silverlight 5 Beta SDK and Visual Studio Tools), you can install the MSI release of the F# 2.0 Free Tools release to enable Silverlight 4.0 or 5.0 development with F# 2.0.