While Luke over at Gizmodo AU wasn't too impressed with the Optimus G, I'm sure for many it's exactly the smartphone you need. If that's the case and you're keen on cracking open its juicy software insides, you'll be happy to know that current variant on-sale in Australia can very much be rooted.
Chris Rowland over at Ausdroid has generously put a guide together that will show you exactly what you need to do to first root the device and if you like, install FreeGee for custom ROMs, followed by CyanogenMod.
The process isn't too complicated, though you might run into trouble getting CyanogenMod onto your Optimus G. As Rowland notes, figuring out how to activate the fastboot and recovery modes took a bit of time and even then, you might need to navigate an invisible menu to get it all working. Fortunately, the Ausdroid article covers the whole process step-by-step, so you shouldn't run into any serious problems.
That said, Rowland does warn that rooting and installing custom ROMs carries some risk, so make sure you know what you're getting into before you start your attempt.