don't override GetPrettyName in nsNoIncomingServer. I was being silly. All I really needed to do was call SetPrettyName with 'Local Mail' to get the desired effect.

mailnews/base/src/nsMsgAccountManager.cpp

@@ -1550,7 +1550,12 @@ nsMsgAccountManager::MigrateLocalMailAccounts(nsIMsgIdentity *identity)
   // "none" is the type we use for migrate Local Mail
   server->SetType("none");
   server->SetHostName(LOCAL_MAIL_FAKE_HOST_NAME);
-    
+
+  // we don't want "nobody at Local Mail" to show up in the
+  // folder pane, so we set the pretty name to "Local Mail"
+  nsString localMailFakeHostName(LOCAL_MAIL_FAKE_HOST_NAME);
+  server->SetPrettyName(localMailFakeHostName.ToNewUnicode());
+  
   // create the directory structure for old 4.x "Local Mail"
   // under <profile dir>/Mail/Local Mail or
   // <"mail.directory" pref>/Local Mail

mailnews/local/src/nsNoIncomingServer.cpp

@@ -41,7 +41,6 @@ public:
     virtual ~nsNoIncomingServer();
     
     NS_IMETHOD GetServerURI(char * *uri);
-    NS_IMETHOD GetPrettyName(PRUnichar **retval);
 };
 
 NS_IMPL_ISUPPORTS_INHERITED(nsNoIncomingServer,
@@ -78,22 +77,6 @@ nsNoIncomingServer::GetServerURI(char **uri)
     return rv;
 }
 
-// we don't want to see "nobody at Local Mail" so we need to over ride this
-NS_IMETHODIMP
-nsNoIncomingServer::GetPrettyName(PRUnichar **retval) 
-{
-  nsresult rv;
-  nsXPIDLCString hostname;
-  rv = GetHostName(getter_Copies(hostname));
-  if (NS_FAILED(rv)) return rv;
-
-  nsString prettyName = (const char *)hostname;
-
-  *retval = prettyName.ToNewUnicode();
-
-  return NS_OK;
-}
-
 nsresult NS_NewNoIncomingServer(const nsIID& iid,
                                   void **result)
 {