In Designer when you create an image of your process (png) or create the process and task form ftl templates, Designer attempts to also store them to Guvnor. Please check your server logs again, even if no exception is thrown there should be some indication of possible failure to connect to Guvnor.
To connect to Guvnor, Designer uses default options provided in $designer.war/profiles/jbpm.xml. Bottom of this file contains:
<externalloadurl protocol="http" host="localhost:8080" subdomain="drools-guvnor/org.drools.guvnor.Guvnor/oryxeditor" usr="admin" pwd="admin"/>
If you are running guvnor on a different host, port or subdomain, or have auth configured and changed the admin user password for example, you would need to reflect those changes in this xml file (which means you need to deploy designer as an exploded war in jboss as).
One more way I can think of to check what is going on in your situation is to use an FF addon like HttpFox and look at all outgoing http connections from Designer to Guvnor, and see what the response codes are..this could also reveal any problems.
Hope this helps.