Well, on love triangles, I would generally agree with what you've already said. I think the prevalence of them in YA which seems to be getting more spotlights these days makes a lot of people want to steer clear of them. I would keep it in terms of conflict. Is it adding something to the story in terms of character development for all characters involved and is it moving the plot forward? If it's just to keep your characters in a constant state of angst back to the drawing board.
Exactly- this is a better way of saying what I was trying to, and an elaboration. If it doesn’t provide conflict in a meaningful way to the story, it’s probably just a cheap way to keep the reader turning pages, to see who he/she is going to “pick”.