I've been aware of the triggers vs. preference divide for a long time, not that it came up much in warning my own fic. (And despite the fact that I have no triggers myself--I have a *lot* of squicks, but it's definitely a different thing.) If anything, I'm glad more people are being made aware of this, and sad that it took a lot of fandom this long to catch on.
My thought, the way I handle this: warn for what you can, and don't worry about the times you might fail (or about really obscure things). Plenty of time to deal with such things when they come up, if they come up--you can be responsible for educating yourself and warning for things you know are likely to be triggery for some people, but you can't be responsible for unusual ones, or for everything. This is, I feel, an acceptable middle ground in my quest to be courteous to all my readers and yet at the same time not allow myself to be consumed by paranoia or unnecessary guilt (which is quite a battle sometimes without adding more burdens to my own psyche).
Examples: I warn for character death (a holdover from my time in The Sentinel fandom, when that was the Rule of Law); for violence beyond what the show would use (and I always warn for torture, even if the show goes there regularly, such as on Alias); I've warned for references to child sexual abuse, and one of my fics has a non-specific "triggery" warning, because I can't specifically warn without giving away the entire plot, but it's the only fic of mine that actually sort of did trigger someone, so it clearly needed something.
I also warn for AU, list pairings, and if necessary list other relevant "genre" stuff. I don't warn for angst, unless it's really extreme.