Under the network optimization FAQ in the IUBE section it says this:
IUBE capability allows users to be placed into various user categories; each assigned a priority for resource allocation. Verizon Wireless deployed IUBE with two categories. The two inter-user priority categories are specified as: Category 0 and Category 1. Category 0 is for those customers who subscribe to unlimited data plans who are in the top 5% high usage customers and are set to receive a smaller proportion of the resource as users in class 1 during periods of high demand within a cell site sector. Category 1 is the default class for typical use.
IUBE has the following effect in the network:
When a user is operating in a sector where demand is not high, there is no effect on the user experience, even if that user happens to subscribe to an unlimited data plan and be in the top 5% of data users. All users receive the same allocation of resources that they would if there were no differentiation of best-effort categories
When a user is operating in a sector where there is high demand, users from each category are assigned resources proportionately, with users in category 0 receiving the lowest allocation. The exact proportions are selectable in powers of 2 (e.g., users in category 1 could get half of the resources assigned to users in category 2, users in category 2 could get half of the resources of users in category 3).*
The actual resource being allocated is forward link timeslots. Because RF conditions determine the actual amount of data that can be transmitted in each timeslot, we cannot state an exact proportionate relationship in the data speeds each user will actually receive. However, if the average of all users operating in a congested sector is considered, it is likely that an average user in category 0 will receive lower data speeds than an average user in category 1, roughly proportionate to the ratio defined. In reality, less differentiation is observed on data speeds among user categories.