Do you ever read more than one book at a time? I do on occasion - I'm actually reading three books right now -- Whispers In The Dark by Maya Banks and Only His by Susan Mallery in paperback and Some Like It In Handcuffs by Christine Warner on my Kindle.
I also like to switch between non-fiction and fiction so often read more than one book at time if I'm reading something for research and something for pleasure.
Do you ever get the characters mixed up from one story to the other? I never have but have a friend who insists she would if she read more than one book at a time.