Backups live in ~/Library/Application Support/MobileSync
iTunes should let you select from available backups, not sure why some aren't showing, it should backup with each sync (by default, I think there is a device preference). If you have Time Machine, it should be archived. You should see all available backups in iTunes > Preferences > Devices.
For some reason, the most recent update nuked my iPad (either that I emit some kind of ray that disrupts iPads) and I had to restore. A lot of app data didn't come back during the restore, most annoyingly the arrangement of apps on the device, which I then had to reorder. I may have uttered a bad word.