Do I read too quickly?

I was just getting into reading a new library book when I was thinking that it all seemed a bit familiar. So I pulled out my reading journal, and discovered that I read it already just last year. I was really pleased to find it in the library as well. So now I am faced with a dilemma. I can't remember the end, so do I keep reading to find out what happens, knowing that as soon as it is finished I will forget it instantly? Or do I just move onto a new book, not wanting to waste time with one that is so instantly forgettable? It's called Vanishing Acts by Jodi Picoult by the way, quite an apt title!

A good book which I can recommend though is The Night Watch by Sarah Waters, that was really good.