Problem: You've just been handed a stack of papers that needs to be signed and returned, and there's no fax machine in sight. You have a pocketful of receipts you're tired of carrying around, and no place to file them. You need to convert a printed document into a PDF.
The solution for all these predicaments is Scanner Pro, which turns your iPhone into a mobile scanner that connects to everything from Dropbox to Evernote to MobileMe. Find the most well-lit setting you possibly can, run the app, then point your iPhone's camera at a document. Assuming you're happy with the capture (a handy Retake button is available if you're not), tap Done, and Scanner Pro converts the page into a PDF. With a few taps you can upload your page(s) to any/all of the aforementioned services, as well as Box.net, Humyo, and WebDAV-compatible online storage.
Scanner Pro also lets you e-mail and print your scans (though the latter requires third-party app Print n Share, which costs $6.99). What you can't do is mark or annotate them; the app's only editing controls are for contrast, brightness, and color/grayscale. If you just want to copy scanned documents to your PC, Scanner Pro provides an always-on network-drive capability; just point your browser to the IP address shown on the app's main page and presto, you've got files.
Unfortunately, it's hampered by the limitations of the iPhone's camera. Our autofocusing 3GS did a pretty decent job of capturing letter-size pages, but we wouldn't call the text razor-sharp. And you really do need a ton of indirect light to get good results. Also, Scanner Pro's interface can be a little confusing at first, and the built-in help is scant at best. We'd like to see business-card scanning and rotation capability as well as greater editing tools. Novice users may find themselves frustrated until they learn their way around. Despite these limitations, Scanner Pro's scanning chops are eclipsed only by its serious pocket-size convenience.