It's happening a lot more often. I purchase a quilt book only to find when I get home that I already have that book.
I found an app called "Book Crawler" that lets you scan in the ISBN barcode with your iPhone or iPad, and it will load that title into a database to keep track of your library. That way you'll always have a list of your books on your iPhone. I'm sure there are similar apps for the other phones as well.
This is also a great tool for insurance purposes. I don't even want to tell you the $ value that mine added up to be. I'd surely never remember all those book titles if a hurricane wiped out my house and I had to file a claim with the insurance company.