Blue/Innovate and Red/Disrupt
An interesting exercise is to work through a product's feature set using both the Strategy Map of "Blue Ocean Strategy" (Kim & Mauborgne) and the disruputive thinking of Christensen.
Blue Innovation creates a new product feature and then makes a market out of it to focus on a new capability -- portable cleaning with the Tide-to-go-Stick, portable computers with smaller drives/better batteries, etc.
Red Disruption challenges the assumptions that 'customer knows' best. Entrants re-order an existing feature set to satisfy part of an existing market that is less than satisfied with current offerings -- Nucor steel made its initial mark by making cheap & fast more important than quality and custom specs, analytic databases trade transaction processsing for user response time, and many packaging innovations in consumer products.
A killer app probably does both -- iPod + iTunes.