Info plugin will show in the admin bar the number of database queries during the WordPress execution and the amount of time in seconds to generate the page. Admin bar can be enabled in your profile:
"Users => Your Profile => Show Admin Bar".
This information also added to the source code of each page. The information is HTML commented for not displaying it in page preview. You can find this information in the the source of the page somewhere in bottom.
Plugin is based on these WordPress functions. You can use them without the plugin.
<?php echo get_num_queries().' queries;'; //echo $wpdb->num_queries; echo timer_stop().' seconds;'; ?>