How can I synchronize multiple devices?

The Book Crawler database can be transferred to another device through the backup/restore mechanism.

The fastest way is to use a single Dropbox account to perform the transfer.  On the device that you want to copy, press Settings -> Import/Export.  Now, press "Link".  Press "Backup" to copy the database to the server.  From your secondary device (the device you want the database transferred to) go to Settings -> Import/Export.  Link to the same account as you did before.  Press "Restore" to replace the database with the one on the server.

IMPORTANT: To merge results with another device, transfer the CSV file.  The CSV file is all text, so it won't be able to transfer images.  To do this, go to Settings -> "Update Entries" to download missing artwork from the internet.  Only transfer the database if you want to replace the database.

If your database is small enough (under 7MB), you can also transfer your data via email.  Go to Settings -> Import/Export and press the "Email" button.

It's also possible to transfer your database file via iTunes file sharing:
http://www.chiisai.com/j25/index.php/general/293-itunesfilesharing

I find using Dropbox on the Import/Export page the easiest to maintain.  I hope to implement the use of iCloud soon which will simplify the process greatly!  My initial tests with it weren't so great as it is a complicated process for a database file.