I built my PC around January of this year and did register my 780 since I was going to do the step-up to a 780ti, but that never ended up happening.
With the release of the 980, is there any aspect of the Step-Up program that 'reactivates' the program with the announcement of a new GPU? I'd love to get the 980 by trading in my 780, but if I can't get it through the Step-Up program, I'll just wait till the 980ti gets released.