gistfile1.js

// promises is an array of jqXHRs or what have you
var deferreds = _.map(promises, function(promise) {
    var deferred = $.Deferred();
    promise.then(
        function() {
            deferred.resolve(true);
        },
        function() {
            deferred.resolve(false);
        }
    );
    return deferred;
});

$.when.apply($, deferreds).done(function() {
    var results = _.countBy(arguments),
        numSuccesses = results["true"] || 0,
        numFailures = results["false"] || 0;
        
    console.log(numSuccesses + " operations succeeded");
    console.log(numFailures + " operations failed");
});