I've tried it for a month and I've gotten a lot better at it. But I haven't really noticed any change in my daily life.
Surprisingly what did help me was to play Starcraft 2. After a month of playing it, I noticed myself immediately attacking any problem in several ways at once, which usually meant I was more effective at solving it. There are a lot of things you have to switch between really fast in SC2, and there are a lot of things you have to pay attention to. It's a lot more engaging and fun, and I think it also improves your working memory.
Holy crap - seriously?
The thing is - it's SO incredibly easy to play Starcraft 2 lazily. Which is why most people don't improve. But if you force yourself to improve, maybe there's a mechanism? I actually posted such a thread here: http://www.quora.com/In-Starcraft-2-how-do-you-deal-with-game-theoretic-anticipation-chains-the-enemy-anticipating-that-you-anticipate-that-the-enemy-anticipate-that-you-might-do-X
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Here was my original question: In Starcraft 2, how do you deal with game-theoretic anticipation chains? (the enemy anticipating that you anticipat...
I've run across a couple of questions about the value of dual n-back, and this is the best place I know of to find people who've worked with it.
If you've tried it, has it noticeably improved your working memory? Was it enough to be worth the time?