На додачу к проблеме тяжести JS, нашел в интернете интересную статью

File File size Gzipped file size
Original jQuery library 62,885 bytes 19,758 bytes
jQuery minified with JSMin 36,391 bytes 11,541 bytes
jQuery minified with Packer 21,557 bytes 11,119 bytes
jQuery minified with the YUI Compressor 31,822 bytes 10,818 bytes

http://www.julienlecomte.net/blog/2007/08/13/