I hate books based only on suspense, so if it looks like that's what it will be, I break it right away by reading the end. If it's written good enough, it won't matter. If not knowing the end is necessary for the book to be enjoyed, that's not a book for me, so at least I don't lose my time.
I mostly like books that can be reread multiple times, so anyway after the first time, I know the end. I also like a lot of classics whose endings are common knowledge. So yep, I read the end first quite often.