My pagebar plugin puts an HTML comment in the frontend (like "pb255") simply for support reasons. People are writing mails about problems with the plugin but forget to mention the WP and plugin versions used. So i first have to ask back, then they anser me and finally I have all the information I need and a fourth mail gets on its way. This can take some days because of different time zones and circadian rhythms. With the comment in the HTML code I'm almost always able to determine the needed version information right away. Security might be an issue I must admit.