This version of cachedGet only allows out one request for each URL. If it's called again with a URL that it's already seen, it adds that to the callback handler for the first request for that URL.

Results

var gPendingRequests = {};
var gRequestCache = {};
$.cachedGet = function(url, k) {
    if (url in gRequestCache)
        k(gRequestCache[url], 'success');
    else if (url in gPendingRequests)
        gPendingRequests[url].push(k);
    else {
        var queue = [k];
        gPendingRequests[url] = queue;
        $.get(url, function(result, status) {
            if (status == 'success')
                gRequestCache[url] = result;
            while (queue.length)
                queue.shift().call(this, result, status);
            delete gPendingRequests[url];
        });
    }
};
$.cachedGet('services/random', log);
$.cachedGet('services/random', log);
$.cachedGet('services/echo/1', log);
$.cachedGet('services/echo/2', log);
$.cachedGet('services/random', log);