I remember the Void Stranger threads on /v/, they were really good about blacking out spoilers and that game has a lot of them. Black Souls threads on /vrpg/ are also really good about hiding spoilers about their plot-with-porn RPG maker game. Nowadays I've had to unsub from anyone playing games I want to play because I've had major things spoiled for me. And yes, Aerith's fate in Final Fantasy R series IS a spoiler because of the nature of the plot.

I also refuse to watch the opening movies in any hentai games because of how many major plot points (including one that didn't get resolved until the LAST game in the series) were spoiled in Sengoku Rance.