Io.9 asks it's readers how long they read a book before they give up on it. I found I couldn't select any of the options, because none of them really describe what I do, which is a pattern of hard-read, skim, skip, drop.
I will hard read the first few pages of a book, which I mean, I'll read every word, from the beginning of the paragraph to the end, and if I can't follow what's going on, I'll even go back and re-read it. There are some books out there that are worthwhile reads, but they just can't be read casually. If you skip a key word in the middle of a dense paragraph, you'll be lost. Some of my favorite books, the ones I reread over and over, require really careful reading.
A couple of things will make me stop after a hard read: if the story is simply unintelligible no matter how much effort I put into it. If it has a really annoying font or stylistic flourish (I had to give up on a book where the author didn't believe in using quotations marks to mark out dialogue). Or if the characters annoy me to the point where I can't give a fuck about what happens to them (PC Cast, yes, I'm looking at you, at least S. Meyer didn't have Bella trashing all her friends and family in the first chapter). But I don't stop simply because the book is boring... not yet.
If the writing just simply isn't that interesting, I relax and begin skimming, rushing to get to where the story actually starts. If later I discover this story is quite exciting after the slow start, I'll actually go back and read that start again more thoroughly. I will skim for a couple of chapters looking for that point where the background has been set up and exciting conflict kicks in.
If after a couple of chapters of emotionally flat scenes it begins to look like this isn't just scene setting, this is the actual story, I do one last ditch attempt to resurrect my interest in the book: I skip ahead. I start reading a couple paragraphs here and there throughout the book, skipping ahead chapters. At this point I don't know what the heck is going on, I'm simply looking for a scene that grabs my interest enough for me to want to stop and read it. I'll read the climax. And then I give up. Usually, by the time I've hit the skipping ahead part, there's really no chance that I really care about the story anyway. I'm just hoping to get some consolation prize for all the effort, maybe a steamy scene or the answer to a mystery. In any case, any residual curiosity is satisfied and I toss the book.
I can't say I've really read the book, I haven't, even though I've read bits and pieces of the whole book.
Weirdly enough, I only do this with original stories, not with fanfic. I'm a ton less charitable when it comes to fanfic -- the writer better grab me in the first five paragraphs or I hit the backarrow button. With fanfic, since I already am sold on the characters and the setting, I know the world and the way it works. So I expect the writer to get to concentrate on being emotionally appealing from the start.