I've done it a few times and it never really spoiled it for me since what I read those times wasn't that spoilery. If I had got majorly spoiled I would've been pissed at myself so I never do it now even if the book sucks. At that point I don't care about the ending at all. I do reread books quite a lot except lately. I've got a huge to read pile right now so I've no time to reread anything. Hell, I've barely got time to read new stuff now.
Me too. For me, unfortunately, I've found that the smart phone is the enemy of reading. I've started to turn it off and put it away when I have reading time.
No but I do usually, early on, glance near the end just to get an idea of how many pages long the book is.
I've never read the last chapter first. Once or twice I've read stories that ended up sucking, so somewhere in the middle I'll just give up, look at the ending, and stop reading, but I'd never read the ending ahead of time for a book I was going to read all the way through.