In a nutshell, you now can:
- Update HTML templates in sitelets without recompiling the solution and see immediate changes
- Use VS in Windows Phone 7 and Eclipse in Android templates, taking advantage of more customization opportunities and IDE services such as an integrated debugger
- Use HttpContext.Current.Session in sitelets and remote/RPC methods
- Use Visual Studio 2011 Beta, .NET 4.5, Windows 8, F# 3.0, even if you do not have the previous .NET framework or F#
For a full change log, please see here.