If like me you are heartily sick of having to disable the 'perform simulation by default' box each time you want to synchronize your database, the secret is to remove 'checked="checked"' from line 218 of

_data/templates_c/p6jhns^b0bb837473df202aec6adfa9e35b2aa569319a6e_0.file.site_update.tpl.php

to give
<ul><li><label><input type="checkbox" name="simulate" value="1"> <?php echo l10n('only perform a simulation (no change in database will be made)');?>

This dry-run functionality should be the exception, not the rule