Haven't seen this flagged / highlighted....and it's worth doing, I think.
The hacked "Maps [brut]" version of Google Maps (and Nav) now works virtually 100%. I installed it on my Nexus One - just like any other app - and drove to Parnell and back. It announced every turn and change at an appropriate and convenient time in advance of the action required. There was some 'funky' repetition of words )"...Continue on continue on to blah st..." and it thinks "Northern Mwy" is pronounced "Northern M-why"...(and "Glenfield Erd" and "Birkenhead Avay"...but that just made it more fun. Best of all - in a childish vein - was "poo-puke erd" (as in chunder). The hacked version works just fine alongside the un-hacked Google Maps, even if it's a different version. It's set up to be an entirely separate app.
It works fine on un-rooted phones. Get it here