I don't generally re-read an entire book. But I will pull a book from my keeper shelf to go back to a particular favorite scene. And sometimes I have been known to get sucked into reading the whole book after I re-read the scene.(SEP's Dream a Little Dream and Hot Shot have both caught me more than once). Not often though, because I am a slow reader and a whole book is a huge investment in time.
I confess--it is the heroine for me. I need to relate to the heroine or the story is spoiled. Not that I don't love the guys--I do. But it really a great heroine that makes the book memorable for me.