I've been using this for the last year or so: I started with Spanish simply because that was all that was available at the time, but I switched over to German as soon as it was available. It's a great community, and any of the downsides are really just due to it being a crowd-sourced enterprise. This means it's free, so I have nothing to complain about! Having said that, there is always room for improvement, so as others say, it's great as a *component* of your language learning. That's the case for everything, I suppose. Oh, and just to clarify in case it wasn't clear to some: it's not just a mobile app. It started as a website, in fact, and it's still there. I used it there and on my iPad, and they are subtly different. For one, on the website, you must type out the words fully rather than simply select them. It trains your brain in a different way, I feel!