Problem: You've just been handed a stack of papers that need to be signed and returned--and there's no fax machine in sight.
Problem: You've got a pocketful of receipts you're tired of carrying around--and no place to file them.
Problem: You need to convert a printed document into a PDF.
The solution for all these predicaments is Scanner Pro ($4.99), which turns your iPhone into a mobile scanner that connects to everything from Dropbox to Evernote to MobileMe.
Here's how it works: 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.
From there, the sky's the limit--or make that the cloud. 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.
I have just two real complaints with the app. First, it's hampered by the limitations of the iPhone's camera. My autofocusing 3GS did a pretty decent job of capturing letter-size pages, but I wouldn't call the text razor-sharp. And you really do need a ton of indirect light to get good results.
Second, Scanner Pro's interface can be a little confusing at first, and the built-in help is scant at best. Novice users may find themselves frustrated until they learn their ways around.
Despite these limitations, I will confess to some serious love for Scanner Pro. Just today I used it to capture and e-mail a few signed pages; the convenience was astounding.
While we're on the subject of camera-powered apps: