I think it's supposed to be "up to 10%" - I have yet to actually see 10% off. I do find the discount is higher in premium cabins though.
The idea is that you would be using it for personal travel - so the discount is only available if you select "Personal Travel" from the program dropdown. "Business Travel" does not show the discount.
I have to book my work flights separately through a corporate travel agency, so I only book using "Personal Travel" on the UA site.