Victor Gaudioso just shot me an email asking me how to debug a Silverlight 4 out-of-browser application where you can just hit F5. I know he is working on his latest Silverlight 4 book so he probably needs to get this in the book tonight.
To illustrate this, I am using the source code for Silverlight Bridge.
1) Right-click on the FileManager project and select Properties. On the Silverlight tab, select Enable running application out of the browser.
2) Build and run the application and install it out-of-browser.
3) Right-click on the FileManager project and select Properties. On the Debug tab, select the application in the Installed out-of-browser application drop down.
4) in the Solution Explorer, right click on the FileManager project and select Set as StartUp Project.
5) Set a break point, Hit F5 and debug!