As a writer, I prefer not to put anything at the top of my story that gives any of it away, especially some story element that I've worked hard to make a surprise or have dramatic impact. However, out of respect for those who do like to avoid stories with WHAMs, I've accepted the need to include a "Story contains WHAMs" disclaimer.
Be that as it may, when it goes to offering up anything more than that - a "The toys will be fixed" or details on the specifics of the WHAM - then I truly do balk. If the reader knows that the ending will be happy, none of the intense emotions I wish to create will be met, IMO.
Therefore, I fully support Wendy's idea. For those who tend to shy away from emotionally intense stories, they can make a quick stop in the WHAMS Warning thread to see if the writer has issued a disclaimer, then determine if the story should be avoided. Perhaps incorporating Yvonne's idea would be an added service - a book-type blurb giving a brief story summary (without giving anything away) might offer readers a better idea about what to expect. Those of us who like to jump in blindly can just avoid that WHAM Warning thread altogether.
On the flip side, writers have to make a concerted effort to leave such a warning, and then I think we can feel guilt-free in WHAMming our little hearts out.
Lynn