Quite a lot, apparently.
I'm quite happy with my new novel The Book of Pain; or more precisely as happy as I'm ever going to be with any of my books.
I did a considerable amount of research to ensure every historical detail was accurate. In fact I researched it to death. Every part but one it seems. The name.
A few days ago I googled it to see if Smashwords or even less hopefully, Amazon had entered it as they sometimes do, and found to my horror that I'm not the only writer of The Book of Pain.
Even one would be bad, but upon further checking I discovered ten books with exactly the same title. I know nothing is unique and everything is just a rehash of something previously written. And even though none of them apart from mine are novels, I really should have checked instead of feeling quite smug and hoping it was unique.