One word: wow
I have used my iPhone 3G for less than a week but I started missing my Pocket PC when I discovered that iPhone/iTunes has no way to copy files to the device. I'm pretty “green“ so I print to PDF instead of bringing paper copies of reservations, directions etc. That worked great on my last Pocket PCs but not on the iPhone :-( Until I tried the free Air Sharing app.
Air Sharing is a very simple application but it fills a big void on the iPhone. It lets you copy any file you want to the iPhone and back. It doesn't matter if the iPhone “supports“ the file format or not. You can view supported formats like html, PDF, jpeg etc directly ...