Possible way of dealing with Meteor collections' insert() not calling the callback when offline. This is code modified from the todos example (http://meteor.com/examples/todos).

todos.js

Template.todos.events(okCancelEvents(
  '#new-todo',
  {
    ok: function (text, evt) {  		
			function doAfterInsert(error, _id) {
				console.log("I was counting on this _id:", _id);
			}
      
			var connected = Meteor.status().connected;
			
      var tag = Session.get('tag_filter');
			var newTodoParams = {
        text: text,
        list_id: Session.get('list_id'),
        done: false,
        timestamp: (new Date()).getTime(),
        tags: tag ? [tag] : []
      };
			
			if (!connected) {
				// Make up our own _id.
				newTodoParams._id = Meteor.uuid();
			}
			
      Todos.insert(newTodoParams,
				// Don't pass a callback to insert if we're not connected, as it'll 
				// never get called.			
				connected ? doAfterInsert : null
			);
			
			if (!connected) {
				// Call the callback directly.
				doAfterInsert(null, newTodoParams._id);
			}
			
      evt.target.value = '';
    }
  }));