a back camera would make the iPad an amazing portable computing device to gather information. I'm currently a geology student and recently on a field trip i couldn't see why all the data collection and processing couldn't be done on an iPad, which would have been more effective modelling and ALOT faster.
also i love to use the iPad as a cook book. it would be great if I could take photos of my creations on the same device that i keep all the info for the recipes.
basically it would make the iPad an amazing data collection and processing tool.