Removing update notifications for non-admins

do_not_nag_non-admins_on_updates.php

/* put this function in your functions.php. You can use it very often */
function __return_null(){
	return NULL;
}

/* stop informing non-admins */
global $current_user;
if( ! current_user_can( 'update_core' ) ){
# 2.8 to 3.0:
remove_action( 'wp_version_check', 'wp_version_check' );
remove_action( 'admin_init', '_maybe_update_core' );
add_filter( 'pre_transient_update_core', '__return_null' );

# 3.0:
add_filter( 'pre_site_transient_update_core', function(){ return NULL; } ); // with PHP 5.3, using anonymous functions
}