An idea of how to refactor

namespace.thumbs.prototype.feed = function() {
    var opts = {};

    return {
        setOptions: set,
        load: load
    };

    function set(opt, val) {
        opts.opt = val;
    }

    function load()
        var ajax;
        if (options.caching) {
            ajax = makeAjax('POST', 'cache.php', 'text');
            tryCache(ajax);
        } else {
            ajax = makeAjax('GET', opts.feedUrl, opts.dataType);
            tryServer(ajax);
        }
    };

    function makeAjax(method, url, dataType) {
        return {
            type: method,
            url: url,
            dataType: dataType
        };
    }

    function tryCache(ajax) {
        $.ajax($.extend(ajax, {
            success: fn,
            error: errFn
        }));
    }

    function tryServer(ajax) {
    }
};

var feed = namespace.thumbs.prototype.feed();
feed.set('context', context);
feed.set('options', options);
feed.set('data', data);
feed.set('optList', optList);
feed.set('listNum', listNum);
feed.set('feedUrl', feedUrl);
feed.set('object', object);
feed.set('errorMessage', 'Vimeo or Youtube thingie');
feed.set('dataType', 'json');
feed.set('cacheFeedData', { host: optList.host });
feed.load();