The official Google Books blog has a fun post on how to scan your books into the service's "My Books" feature by using a USB barcode scanner. The My Books section of Google Books is similar to the popular Mac application Delicious Library in letting you keep a list of all your titles in a digital card catalog that can be shared with others. Of course you can do this without the USB barcode scanner simply by searching for the book, but Google's Matt Cutts makes it look like fun:
As Cutts mentions in the video, one of the benefits of building up your Google Books library is that you can limit in-text searches to just the titles you own. Not mentioned, however, is that it's a great way to build up a personal effects value estimate for insurance purposes.
Having recently given away an entire bookshelf while doing some spring cleaning, using a system like this would have made it easier to keep track of all of the things I've read throughout my life. This is something that the Kindle and other e-book readers can provide for future generations of readers without as much elbow grease.
If you don't feel like giving all that personal information to Google you can also use some other Web services to do this, including Shelfari, GoodReads, and Library Thing. However Google's big ISBN entry screen is the most barcode-friendly of the bunch.