I did a quick search but there was no real feedback as such for this specific suggestion. It came to mind after looking at Sy's Anime thread that this forum doesn't seem to have a "spoiler" option, you may have seen it from time to time in other forums.
Basically it adds a button to the post where it's used that says "show spoiler" and when you click it it uncovers whatever text the person in question tagged, much handier than people having to recolour text white or whatever to avoid giving things away by accident.
Probably not top of the agenda but I reckon it'd get some fairly significant use