tumblrGists.js

var gistPrefix = 'https://gist.github.com/',
    cachedWrite = document.write,
    body = $('body'),
    gists = $('p.gist').map(function(n, p) {
        p = $(p);

        var a = $('a', p),
            href = a.attr('href');

        if (a.length && href.indexOf(gistPrefix) == 0) {
            return {
                p: p,
                id: href.substring(gistPrefix.length)
            };
        }
        else {
            return undefined;
        }
    }).get(),
    embedNextGist = function() {
        if (gists.length == 0) {
            document.write = cachedWrite;
        }
        else {
            var gist = gists.shift();

            document.write = function(styleLink) {
                document.write = function(gistDiv) {
                    gist.p.replaceWith(gistDiv);

                    embedNextGist();
                };
            };

            body.append('<scr' + 'ipt src="' + gistPrefix + gist.id +
                '.js"></scr' + 'ipt>');
        }
    };

embedNextGist();