A while back, we talked about using the RTA metatag and logo on sites to indicate a site that is "Restricted to Adults". There was mixed feelings about it's effectiveness and use. I still think it's a good idea to at least show a site is trying to keep kids out.
I object to this sort of thing just on the basis of the concept of the "WordPress way" making everyone HTML-ignorant. Just open the header.php file in your theme and add the line there. Sheesh!
Yeah, I know that if you update at some later date your theme you'll have to re-edit the code, but it's just as likely all these plugins will need updating, not counting the updates to WP itself, plus it's just another bit of active code that could have an unintentional exploit it in.
Not sure that I object to it VG, but totally agree with you that everybody should be able to just open the code up and insert something like this. This one is about as simple as it gets.
Reality though, is that there are a LOT of people who know little to nothing about code and it's good to have options for those that have not figured out that they really need to know this stuff.