using jquery ui tabs, when you load a tab in ajax, the tab changes message to say "Loading . ." i think this is a little subtle.
Is there anyway you can do something in this content area of the tab similar to what block ui does when you are loading a call in ajax.
You would display a loading message within the content area like so (untested):
$('#selector').bind('tabsselect', function(event, ui) {
// show default $.blockUI loading message
$('ui.panel').blockUI();
}).bind('tabsload', function(event, ui) {
// remove loading message
$('ui.panel').unblockUI();
});