We have a number of first-generation iPhones fully unlocked and jailbroken using Pwnage from the iPhone Dev Team. (The iPhone 3G is not currently software-unlockable with any degree of reliability.)
One of the challenges for both 'official' (installed from Apple's App Store) and 'unofficial' (using installer.app or Cydia) apps that create content (photos, videos, text etc) is how to share the content. One approach taken by several apps is to offer to send an attachment via email. While this is fine for text files and photos, it's not so appropriate for larger files like video. You could also install OpenSSH and use scp to get the files, but that involves opening up root access which I didn't want to do for users who are a bit less tech savvy.
Here's our particular problem and solution. I have installed the Cycorder app, which allows you to capture video, but relies on scp and a knowledge of where the files are to move files off of the phone. By a bit of experimentation, I have managed to change the location where Cycorder saves its files. By changing the save location, I can then share/delete videos using Air Sharing (an 'official' app from the App Store). The general technique could also be useful for other applications.
Here's what to do; I'll assume that you have a Jailbroken iPhone, so Cydia and installer.app are already available. If not, go and jailbreak.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081001062146896