http://www.tjkelly.com/blog/remove-wordpress-jetpack-css/

gistfile1.txt

function remove_jetpack_styles(){
wp_deregister_style('AtD_style'); // After the Deadline
wp_deregister_style('jetpack-carousel'); // Carousel
wp_deregister_style('grunion.css'); // Grunion contact form
wp_deregister_style('the-neverending-homepage'); // Infinite Scroll
wp_deregister_style('infinity-twentyten'); // Infinite Scroll - Twentyten Theme
wp_deregister_style('infinity-twentyeleven'); // Infinite Scroll - Twentyeleven Theme
wp_deregister_style('infinity-twentytwelve'); // Infinite Scroll - Twentytwelve Theme
wp_deregister_style('noticons'); // Notes
wp_deregister_style('post-by-email'); // Post by Email
wp_deregister_style('publicize'); // Publicize
wp_deregister_style('sharedaddy'); // Sharedaddy
wp_deregister_style('sharing'); // Sharedaddy Sharing
wp_deregister_style('stats_reports_css'); // Stats
wp_deregister_style('jetpack-widgets'); // Widgets
}
add_action('wp_print_styles', 'remove_jetpack_styles');