This Flickr image set does a nice job of pointing out the unique UI elements of the iPad. Much of the interface is adapted from Apple’s extensive work on the iPhone but there are several unique elements.
Say what you will about Apple (positive or negative) but their tight reign on software and hardware and extreme focus on details really shows.
On a separate note, while I probably won’t be getting an iPad, the use cases illustrated in the keynote video are very compelling (e.g., imagine using this as a data collection device in the field). I just can’t see myself lugging around a third device.