The premise behind DriveDroid is simple. It turns your phone into a USB drive. The application can either use an ISO file (e.g. to make a Linux boot CD - the application includes links to download these from the app itself) or you can create 'empty images' which effectively turn your device into a fully read-writable USB stick.
I tested the application with both those different scenarios - I booted Ubuntu on my machine using only my phone and a microUSB cable and I plugged my phone into my Mac whereby it appeared as an empty USB drive (100MB, because that's the capacity I chose) and I was able to copy files to it, unplug, then plug back in and pull the files off. Awesome!
The application is available in free (ad supported) and paid (80p) versions, although it's recommended that you download the free version to check compatability with your hardware before purchase.
I tested using my HTC Butterfly - all good - let us know how you get on!
Click here to view the item