There's a lot of fuss being kicked up about spoilers in Avatar fandom right at the moment. Fuss that could have been avoided if Nickelodeon had removed their fucking head head from their ass and aired the episodes on a sane schedule, but that's a whole other matter. A lot of people are going underground altogether to avoid spoilers, but my stance on the spoilers is thus:
I don't really care about spoilers.
To clarify: I don't like spoilers. I'd rather walk into the new episode with only a trailer's worth of knowledge about what's going to happen. But if I happen to be spoiled, then, well. It's not a big deal. I'll still enjoy the episode almost as, if not exactly as, much as I would if I had watched it unspoiled.
Now, obviously, this varies depending on the spoiler. If I get hit with a spoiler like 'AZULA KILLS SUKI AND SOKKA GOES BERSERK AND KILLS HER' or something, something major and important and unexpected, I'll be a lot more pissed off than I would be if I got a spoiler like 'SOKKA FIGHTS A ROOM FULL OF FIREBENDERS AND WINS', which just describes one scene that isn't going to affect the overall plot that much. Actually, that last one's probably a bad example, as that spoiler would have me spinning with glee and anticipation, but you get the idea.
It also varies from canon to canon. Avatar spoilers bother me more than One Piece spoilers do, because One Piece's plot (although awesome) tends to run in a pretty straight line and it's really the ride that I'm invested in. I don't really want spoilers for the plot of an individual Doctor Who episode, but if the episode's place in the overall plot of the series is spoiled, I don't really care, because I'm more interested in the Doctor having his little individual adventures with Martha/Rose/Donna than any sort of overall arc. Anyone who spoils the next Song of Ice and Fire book for me gets his hands chopped off, because the best part of those books is not knowing what's coming up. Naruto spoilers...from the way the past year or so of it's gone, I'm probably just going to shake my head and disgust and say 'Yeah, that sounds appropriately stupid. Let me guess, still no Chouji or Rock Lee, right? Yeah, that's what I thought...'. Similar situation with my spoiler experience with the last Harry Potter book.
So, you can tell, there's not really any real system to it. Individual shows and manga and whatnot each have their own spoiler value, and there's no way to predict what will and what will not bother me in terms of spoilers.
A few more quick points:
1. People who spoil other people deliberatly? Assholes. Complete and total assholes. It's just trolling, straight up.
2. If I see spoilers on /co/ or fansites or whatnot, I'll try to look away, but I accept that that's a risk I take for frequenting them.
3. Someone on my flist (not naming names. Not because I want to protect their identity or anything, because I honestly can't remember who) said that you never enjoy something as much if you're spoiled, and I don't think that's true. For example, I had every single one of the major epic speeches from Tengen Toppa Gurren Lagann spoiled for me ahead of time, word for word. But that actually enhanced my enjoyment of the show, because I had no idea of the context on those speeches. So when I saw what the context actually was, I would squeal out because it was invariably way more awesome than what I was expecting. That's obviously a case-by-case sort of thing, though.
4. If something's been out for a year or more...I'm sorry, I don't have much pity if you get spoiled. =/
5. Although I don't myself understand the mindset that spoilers absolutely ruin everything, I do respect it. Spoilers on my LJ always go behind a cut, with warnings.
6. That said, I'm really horrible at thinking before I speak and so sometimes I'll blurt out stuff that is spoilers without realizing it. =/ SORRY GUYS. I'm generally pretty good, but it happens occasionally.
So yeah, that's my stance on the whole scenario.