Yes, the fee system does seem a bit iffy to me. Will miners make enough from it to be worth keeping their mining operations going? If all but a few miners drop, won't those few have control of a significant portion of the network's processing power? How will users know what's a good fee to add to each transaction?
It kinda bugs me especially that the fee is set to zero by default, since a lot of people probably won't bother to change it. 0.01 might be a saner default. I doubt people are going to complain about such a small fee that they can disable if they want, but enough will leave it on that there should still be a decent amount going around.
(Just make sure people know it's there - they're likely to get angry at a "hidden fee", even if it can be disabled and no matter how small it is.)