See, there are two types of spoilers.

Like. He ate some cheese in -insert thing here-...you still don't know why he ate the cheese.

Yes, it's a horrible example, but it's the only thing I could think of that didn't spoil something. So, apply it to something you've seen to where it tells what happened, but not the store of HOW everything got there.

I lied, spoiler time if, for some reason you have never read/watched/heard of LOTR

The ring is destroyed. Oops. I told you the end. But did it spoil it? No, because you have no idea how it happened. You have no clue whatsoever.

I used to get really annoyed when people spoiled something for me, to the point I wouldn't even finish it. (Like Assassin's Creed - ended up playing the series 5 years later and loving it though)

But here recently I just don't care. I had Shingeki no Kyojin spoiled very early on, to name something recent. I had specifically told that person not to say a single word, but they started telling me major spoilers from the manga in detail. +shakes head+

But, yeah, if I happened to be spoiled, oh well. I still refuse to tell spoilers to others though, out of respect for them. It's just rude to ruin something for someone, even if it's minor.

I really dislike them if they're about a book/game/movie that I really really want to read/play/see... I feel it takes away from the story, for me anyway.

For me it depends on the nature of the spoiler. If it's a key plot point I'll mind the spoiler, especially if the whole thing gets spoiled. Like before I read the Half Blood Prince I heard that Snape killed Dumbledore, but I didn't hear why he did, though that wasn't explained until the Deathly Hollows anyway. xD If it's a spoiler that's just simple thing, I don't mind it at all. For example in Pokemon X and Y I already know that there will be new legendaries (dun dun dun!). It's not a big deal since it's something I pretty much knew would happen.

Depends on the spoiler
and how important the thing is to me
I was super amendment about Pokemon spoilers
pertaining to anything not on Serebii's site
Especially Chespin's final form (boy was I surprised last night)

A lot of things I don't plan on reading/watching/playing I don't mind spoilers for
Attack on Titan is pretty much spoiled for me, my husband is into it as are some of my friends
and I honestly don't think I'll ever have time to watch/read it so I don't care
Or like the ending to Harry Potter, I still haven't watched the last movie
but I know how it ends for the most part and some day I will watch it

I try to make sure to either label my spoilers or make things as vague as possible
Sometimes spoilers do slip out though but it's usually because I don't consider that thing a spoiler really

I don't really mind tha much if someone spoils something for me, but people get really pissed if I spoil something for them. I don't get it.

I'm glad there are spoiler tags now too. ^^ The old method of making the words white was okay, but having a spoiler tag makes things neater.