My Nokia 6300 behaves like a flash or thumb drive when I connect it to a computer using an USB cable. I think this should be standard functionality nowadays. Cellphones are replacing the Filofax and MP3 players. I can read mail on my cellphone, take pictures and movies. It contains an 4GB memory stick, sometimes even more. So why do I need to carry this silly thumbdrive with me?
If you have an iPhone with the 2.0 firmware, unlimited dataplan, and maybe even MobileMe, you may already have found a solution for carrying all kinds of data with you. If you haven’t, maybe DataCase is something for you. It will allow you to turn your iPhone into a (network) drive and put stuff on there to take with you.
Please note that at the time of this writing, DataCase is in closed Beta testing.
There seem to be more apps that do this. One of them is PhoneView, but it requires installation on your mac: http://www.ecamm.com/mac/phoneview/instructions.html
The best option in my opinion is still having the iPhone do all the work, because maybe you need to drag a file to a computer which is not yours.