If you are using the web designer within Guvnor as shown in demo video http://people.redhat.com/kverlaen/install-guvnor-jbpm.swf, you don't have to worry about assigning an unique uuid as Guvnor will do that for you. If you are using web designer standalone then you have to give your process an unique uuid yourself (by setting uuid parameter as shown before).
Guvnor only stores the process bpmn2. If you use web designer in standalone mode, then only the json will be saved.
With this release we are using the latest version of web designer so yes there are some differences from the older versions.
Thanks.