Since we released our preview at MIX, there have been a fair number of questions revolving around how a WPF or Silverlight project that uses Blend-specific features will work when opened on a machine that does not have Blend installed. For example, one Blend-specific feature that we have talked about extensively is Behaviors. The Behaviors runtime components are provided to you by Blend, and today, there is no way of being able to author or build a project that uses them without having Blend installed.
To help address this concern, we have been working on creating the Expression Blend 3 SDK. The Blend 3 SDK is a free (and lightweight) installer that places common components such as Behaviors into a general location that other applications like Visual Studio can access. This gives you the ability to open and edit projects created or modified by Blend without having to have Blend installed on your computer.
Before wrapping up this post, I should emphasize that you will only need the Blend 3 SDK to open projects that contain some runtime component that is Blend specific and you do not have Blend 3 installed. That means you can open a cool Behaviors project or even write your own behaviors using just Visual Studio and not having Blend installed on your machine.