I'm skeptical of the claim that brain training (dual-n back) can improve working memory; the improvement seems to be task-specific rather than generalize.
The average human being can only keep 7 things in his or her mind at one time. Brain training claims to be able to increase this capacity, but as said above, I am skeptical. Are there any studies that have have shown that the 7-limit short term memory capacity can be increased? Of course, we can abstract and have an mnemonic stand for seven things, but we are still only holding one thing (the mnemonic) in our minds..