While the iPhone's keyboard is easy to use, your camera is often a faster way to take notes. Taking photos of a whiteboard or blackboard can save you a lot of typing time. The 2 megapixel camera has enough resolution that you'll be able to see everything.
Don't clutter your pockets with business cards. Take a photo and hand it back. When you have time later at home you can enter it into your desktop contacts. Or if you go to a great restaurant, snap the menu. You can use your camera to capture screenshots or anything that you'd use a scanner for. The advantage is that you can even "scan" posters on the wall that you can't get into the scanner. Decent OCR software may even be able to characterize notes for you.
Faster Notetaking w/ your Camera
