Minifying+concatenating is the most appealing solution for desktop browsers which employ a rather large cache on static files, considering that a web server is also fine-tuned to take advantage of caching (e.g. http://httpd.apache.org/docs/2.2/mod/mod_expires.html). I am not sure though that this is the best approach for mobile devices; having to serve a relatively large JS/CSS file with (possible) network interruptions may increase page load time.