We have edited out serious spoilers in titles in the past, I'll use one of my own questions about Mass Effect 3 as an example.
My original question contained a spoiler about a character dying in the title. At the time I didn't consider it a major spoiler as I thought the death of the character was preventable, like with other characters in the game. I was wrong about that in this case, and there was some backlash against my spoilery title. It was changed, and while I don't like using less useful titles that are harder to find by searching, I certainly understand why avoiding the spoiler was probably the better choice.
I'm not particularly sensitive with regards to spoilers, I think too many people exaggerate their negative impact. I'm especially annoyed when people complain about very minor spoilers that are almost impossible to avoid. The only sure way to avoid all spoilers is to avoid the entire internet, or at least any site that covers this particular game.
I think we should make an effort to avoid major spoilers in titles and excerpts. Otherwise this site is useless to anyone that cares even a bit about spoilers, as the danger of being spoiled is getting rather large. For newly released games, I think avoiding major spoilers in titles makes a lot of sense. If we don't do that, there is a huge incentive for users to avoid reading the site at all while they play. This hurts the site as those users won't ask or answer anything, just because they don't want to be spoiled. There is a price to pay for this, and that price are bad titles. If we avoid spoilers, our titles are going to be worse. I think that is a reasonable price to pay for major spoilers for current games.
One part of avoiding spoilers is common sense. For example, if there is a question about the ending of a particular game, why are people complaining about getting spoiled when they read that post, or why do they complain about the lack of spoiler markup in the answer? If you don't want to get spoiled, you certainly shouldn't read any question that mentions the ending of the game. The important part is preventing the unavoidable spoilers, which are mostly the question titles. Those appear on the main site, in chat or even in the hot network questions. We shouldn't put major spoilers in those titles, even if it hurts the ability to find those questions via search engines because we have to choose crappier titles to avoid the spoilers.