i spoke to a few travel agents..
visa on arrival is subject to a few conditions.. one a return/onward ticket.. two, sufficient finances for your stay in HK. that when i clarified means; either have an international credit card, or 300usd per day X no of days in HK.
your hotel bookings are not really required. the part of the finances too.. they do not ask everyone. but thats the requirement, so they could check.
he also suggested carrying a photograph just incase.
cheers!