Extremely useful Ruby strategy courtesy one of our friends in Gods Of War.
There happens to be 2 kinds of usage discount - the personal discount comes in case a person hasn't spent rubies for quite some time (around 2 weeks) OR to initiate a non-ruby player to buy some. Apparently there's some kinda algorithm for this
The general discount is the one that appears for everyone's profile. Its a really great thing coz it helped me max out the ruby constructions at most of my points - brought @75% & used at 50%.
So Ruby buyers, bottom line is Buy when you have 75% sale and then dont spend even a single ruby till you get the 50% discount.