A Cre8asite Forums poses an interesting question regarding social responsibility. If you have a site that requires age verification and you want to keep the content away from people who are not of age, what can you do?
The best solution offered is to hold true to your concerns of social responsibility and keep the content from search engines just as you would from users.
But I think that has to be carried over to the search engines, too. If you can't show your content to underage surfers then the engines shouldn't show it to underage surfers either. And that's exactly what will happen, via snippets and cached pages, if the site is indexed.
So that seems to be possible, by using the following directive:
<META NAME="GOOGLEBOT" CONTENT="NOSNIPPET">
Forum discussion at Cre8asite Forums.