People don't often think about digital cameras and camera phones as business tools, but they are. They can photograph business documents for later reference. I use my digital camera all the time to capture whiteboards, for example. The problem is figuring out what to do with the pictures. A relatively new service, ScanR, processes these images for you and makes them highly useful.
To use ScanR, e-mail your picture to the service (email@example.com for whiteboards or firstname.lastname@example.org for other documents). A few moments later, you get back a PDF version of your picture. The image is cleaned up; the contrast is adjusted to make text readable, and skewed text is straightened out. The service also does an OCR (optical character recognition) run on your document and embeds that data in the PDF. The OCR isn't nearly good enough to paste into a text document, but it is good enough for a desktop search engine to reliably index your file. So once you park the PDF in a corner of your hard disk, you'll be able to find it again.
I tried the service using images from my digital camera, but the best way to use this is with a camera phone: Take a picture of a whiteboard, send it immediately to ScanR, and later when you get back to your computer, you'll have a nice clean, OCR'd version of it waiting for you. (You could even set up an e-mail filter to have the attachment automatically stored on your hard disk, I suppose.) I can imagine this application also being very useful for students, for recording whiteboards or chalkboards (do they still use chalkboards?).
A business card application is coming in the summer. This will be, theoretically, better than one of those dedicated business card scanners, since it won't require you maintain yet another piece of hardware. You'll be able to photograph just one card, or a bunch laid out on a table, and the ScanR service will parse them into vCard contact records.
By doing the heavy image processing and computing in its server farm and not in the puny brains of cell phones, ScanR makes camera phones appear much smarter than they really are. The service is free for now, but there will eventually be a premium, paid component for people who use the service more than occasionally.
The one downside: ScanR requires a 1.3-megapixel camera to record whiteboards and 2-megapixel resolution for printed documents. Geeks with Treo 650s are out of luck.