FWIW, I've recently set up 2 US Series 1 Tivos using the 1.6.2 Oztivo image (postcode 02113; Sky Digital Akl; GS'd to 8000 emulator) - one gets guide data via turbonet card, the other via dialup. Both have been working solidly since (great work guys!).
Jeremy (bigmal): so you shouldn't need to go back to 1.5. Lemme know if you need more info...
Cheers,
Marty.