Meet Fly. We had so much fun playing with it, we made a video explaining what it was using the nifty little app, which is free and available in the iTunes store. It's a streamlined tool that allows you to easily film and assemble video using multiple cuts all from your iPhone. It supports gesture control (swipe quickly between cuts for a fast transition; swipe slowly for a nice dissolve), as well as side-by-side and picture-in-picture capabilities. Basically, you can stitch your cow trombone sessions into beautifully edited vignettes.
As an awesome extra feature, you can also sync multiple phones' videos together, so you can easily shoot from different angles — which means that any amateur filming you are doing suddenly gets all sorts of new perspective. Broom broom!