Well, one of the books my Kindle's previous owner left for me was "Marley & Me" by John Grogan. It wasn't something I'd been planning to read.
But I just finished it, and
man, did I ever have to scramble to explain to my boss why tears were rolling down my face when I returned from the ladies' room!
And if the p/o hadn't left it for me, I probably would never have read it! So don't delete those "leftover" books just yet - you never know, they might be something you'd enjoy.