Thanks guys. It'll work on any iPhone or Touch Jailbroken or not. But as it's still a beta release its not in the App Store yet. If you want to give it a try DM me, or email, your UDID and email address and I'll add you to my devel account and email you the application. It's perfectly legit this way too btw!
Yes, you can find out how far you are, just like any other marker in the Maps app, there's still a LOT to do to it and once iPhone 3.0 is released it lets me do new things by embedding the map and using custom markers etc.
If you want to try it, here are instructions from Apple to get the UDID
You can also find out your device’s UDID using iTunes 7.7. or later. To do this, connect your device to your Mac and launch iTunes. In iTunes, select your device in the ‘Devices’ section and navigate to the Summary tab. Click on the Serial Number label to reveal the Identifier field and the 40 character UDID. Press Command+C to copy the UDID to your clipboard.