The folks in the .NET Framework Setup team have a favor to ask, and it's pretty cool info so I offered to help. Here's the deal. When .NET 4 releases, the .NET 4 Client Profile will be released as a recommended update on Windows Update (WU) for Vista and Windows 7. It'll be listed as optional on Windows XP. They need help testing the WU parts. You may have heard, but the .NET 4 Client Profile size is WAY smaller than before. There's been lots of cool improvements since the .NET 3.5 Client Profile . For example, on Window XP the download for .NET 4 Client is just ~28Mb for machines with no framework. .NET Framework 3.5 SP1 Client Profile .NET Framework 4 Client Profile Web install only Local package and Web install. Only Windows…(read more)