If you'd like to see what people are doing with Plumtree on the open internet, you can search Google using the allinurl: portal/server.pt syntax.
Bear in mind that Plumtree portal administrators can change both "portal" and "server.pt" to anything, but most do not choose (or do not know how) to change this. Really, it's easy -- just change the VirtualDirectoryPath and the HTTPEntryPoint in j_config.xml or n_config.xml.