The repository includes Eclipse project files so you should be able to import it without too much trouble. It also needs at least GWT and the IT Mill Tookit jar. It looks like the build script for building the widget sets is missing though.
Not yet. We have been really busy with 5.2.0 release, but after it Coverflow will be promoted to be an example in standard distribution package and thus will be deployed to our demo-server: http://dev.itmill.com/ticket/1691
Meanwhile - the example application in incubator is fairly easy to set up. Just try it out :)