I can put down a book and not read it for several weeks, especially if it is non-fiction. However, if it is a really good book and/or something that interests me, I can hardly put it down to go to sleep at night !
I do this quite a lot, I stop about 3/4 the way through a book (if I don't read a book in large chunks or read it every day I tend to lose interest in it) then return to it months later and start reading it as if I've never stopped. I don't reread what I've already read, I find the story springs back to mind as soon as I start reading again.
Chances are... If I put a book down for a few months... then I am not interested in finishing it. lol In the rare chance that I leave a book and DO want to pick it up again... I usually start over. There is always something little that ends up being important that I forget. :3