We don't need some warning on the Main Page for "protecting" sensitive eyes - that is just plain silly. As somebody already mentioned the vast majority of hits we get are through external search engines that bring viewers to individual articles. Also if the viewer has parental controls on while using the external search engine then they won't land on any "objectionable" Wikipedia articles.
How about this; Have a link in the footer area of each page that simply says "Disclaimer and Copyright Notice"
Then we could have a general disclaimer (as most large websites do) that can say several things;
1) We could warn people not to depend on Wikipedia for data that will be used to design intergalatic probes, find cures for cancer or operate on kittens because we can't make any promises as to the accuracy of the information we present in spite of the fact that most of us try our best to write excellent and correct material (also a disclaimer of legal liability would be nice). 2) We could also state that part of our mission is to describe works of art in a comprehensive mannor so we will be giving away plots and the endings of stories. 3) In addition we would also state that our intention to to cover all human knowledge of encyclopedic value and this includes material that some people may find to be objectionable or even offensive for various reasons.
No need for meta-tag based filters and no need for a message on the main page that hardly anybody who might need it would ever see.
-- Daniel Mayer (aka mav)