Supermemo was designed by a scientist, and a simple user interface is not as high on the priority list as optimized algorithms, incremental reading, etc. I highly doubt that outside of Supermemo a more effective flashcard software exists. Thus, to make flashcard-based learning hit critical mass, it must be packaged in a way that is extremely appealing and fun (Aside from the joy of learning) so that people can survive the two-week "hump" that most people stop using Supermemo. Other than a game or a more aesthetically pleasing UI, I think we're kind of stuck with our present situation, unless a higher authority (Education system, government) makes such learning techniques mandatory, which will not happen due to the inefficiency of modern institutions to fulfill their explicit purpose. At least they exist for the self-motivated to use, and it gives us a mental edge on those that do not use (Or care to use) SRS.

Supermemo has been working on this problem since 1982, and they struggle to make Supermemo popular because it is not "sticky" enough. Basically it involves hard work for future benefit. This is the mental equivalent of "earning an honest living," or "getting rich slowly." We do not live in a world that portrays honest, slow but meaningful progress. We live in a world that is obsessed with instant gratification, and SRS methods go contrary to the river-like "current" of this system. See: http://wiki.supermemo.org/index.php?title=Why_isn'tSuperMemomore_popular%3F Also, the only way I could see SRS hitting massive appeal is if it were designed from the ground up to be a game of some sort where doing flashcard repetitions resulted in progress. I have an idea of how it would work, but I doubt we will see anything like that for the time being.