My trusty iPhone 3G has done me fairly well over the past few years but the more time goes on, the more demanding I am of the little sucker.
I have wanted a native background Google Latitude app for a while now but the only offering seemed to be a $2 application in the Rock Your Phone app store called "Longitude". Sure I could have paid for the app but I figured I was due for a bit of self-study and having never written anything using Objective C, the latitude API or OAuth before, I set about reading. A few days of tinkering later and the app is fully functional! How unexpectedly painless. :)
The actual location handling code on the iPhone side is mostly thanks to Chris Alvares and his very useful tutorial on writing an iPhone Daemon. (Thanks Chris!)
You can access the source code for both the appengine side (OAuth, Latitude API) and iPhone side (setup application + background daemon) at github.
My next step is probably to get it pushed into a cydia repository somehow. (i.e. More research.)
PS. I also half suspect I'll receive an email from Apple's lawyers demanding I change the applications name but time will tell. :)