This is an important bit of kit for the iPad, because it lets you plug in a serious camera such as a Nikon D3
, download the pictures, email them, upload them, or whatever else you want to do, and get on with shooting. For a professional photo shoot on location, it means you can check the images for focus and other flaws on a bigger screen without having to pack a laptop. Nikon used to sell a dedicated device for that, at several times the price of an iPad.
Since the advent of iOS 4.2 you can also use the USB connector for midi connection, with the appropriate app, and it can also (again, with the appropriate app) be used for getting sound in and out. Other uses are bound to follow, since Apple has obviously left some of the protocols open for this device.
All in all I'm very pleased to have this, though I would quite happily accept the USB port only, since I don't use SD cards. This appears to be priced at the bottom of Apple's range, though, and they may have decided that users wouldn't want it if it were just the USB.
When you see how small it is, you may baulk at the price. When you begin to use it and discover how useful it is, that price begins to seem irrelevant.
Recommended to all serious photographers who use an iPad.