I could have sworn I haven't read this

There are occasions where I have read a book and then forgotten that i read it, until I picked it up again and got halfway through the book wonder why I know what is going to happen next. This usually happens with series that have long stretches of time between each book.
The most recent of these is buying "A Storm of Swords" by George R. R. Martin three times, reading halfway through it, then realizing 1.) I've already read the thing, and 2.) Oh, look, there it is on my book shelf. Luckily, the bookstore has understood each time, and the book was in good shape, so I was able to return it. One of those times to a cashier who was laughing her ass off at me (Thanks, sis).
This does not happen often with me, as I usually know exactly what books are on my shelves at home. I mainly run into picking up the same book over and over again at the library. Or wondering while I'm there if I've read a certain book. Or my husband asking my opinion of a book we both know I've read, but can't remember reading it.
So, I've decided to start keeping track of the books I've picked up to read, and the one's I've actually read. Maybe even comment on those I have read. Maybe. Quite honestly, my book reviews have only ever made sense to me; made it hard to get passing grades on those book reports in school. The last reviews I gave hubby of a couple of books:

King Dork by Frank Portman - Put yourself in the mindset of a teenager and read. You'll laugh your ass off. Will be a good read for TeenD when she stops thinking kissing is gross.

The Road by Cormac McCarthy - Do Not Read If Prone To Depression And/Or Suicide. Seriously, by page 5 I was contemplating finding the good kitchen knife and taking it to my wrists. I didn't even attempt to make it to page 6, and just took it back to the library. It still took me several days to pull myself out of that depression.
This book is now on my very short list of books I've started, and will never finish. I believe that list is only 2 or 3 books long. (I'm kind of anal about finishing a book I start. I keep thinking that it will get better.)

Funniest multiple book purchase ever Award: Goes to my Mother!
One year I got the same book from my mother 6 times. That's right, she bought and wrapped the same title 6 times and never caught on until I opened them Christmas Day. It's even possible she picked up two of the copies in the same trip.