You use these adapters to transfer images when you’re away from a computer with which the iPad syncs. You can view imported photos and videos at full scale, or use Photos or third-party apps to upload to various services, like MobileMe or Flickr. Photos lacks any way to send or upload multiple photos at one time, a silly limit for software that can import images. Some developers offer apps with multiple-picture upload, and I expect we’ll see more targeted more precisely at those who import photos to iPad.
It would be nice to see some more uses for these dongles — hopefully Apple and 3rd-party developers will write more software that could use that USB port — or even an SD card — for some uses other than just importing photos.
Some have had luck connecting a USB keyboard to the iPad via the USB dongle, meaning it is only a matter of time until I try hooking my Apple Extended II keyboard to my iPad.