(answer to the question "Is Brain Training fun, fad or a little of both?" and various softwares for soft brains)
To me it's like training in a gym, following a program while checking your heartbeat and the number of calories you're presumably burning... It can be fun and even make sense for people under reeducation, for medical purposes... but this isn't the real thing.
You want to err in open spaces, off the path, work things out with people instead of softwares and machines. Brain is one thing, intelligence another. Try to stimulate your intelligence instead of training your brain. And diversify your programs - reading a good book, listening to great music, that often beats your DS provided you open your mind beyond your eyes.