Quantity discounts are hugely important to me (and anyone else in the printing industry, among others). Right now to the only way to implement this is with a kludgy work-around where you set quantities using an option field, or maybe do something really complicated with calculation fields. I haven't gotten it to work yet.
However, it seems like an easy way to implement this would be to add optional price fields when you have a quantity field dropdown (the same as enabling values with an ordinary dropdown). This would not be as robust as a solution that lets you set up a price matrix (users are limited to quantities in the dropdown), but is should be an easy quick fix.