Marius, you are one of many that was severely hit by Panda. I truly hate to be the bearer of bad news, but I think it's important to devote as much time as you can seeking alternative traffic sources, as there is a strong possibility that you will not regain your Google position anytime soon, if ever.
Tedster has said in another thread that there is some evidence of some recovery by some people, so I suppose there is some hope, but it's hard to pay your bills on hope, so again, IMO the wisest course may be to immediately prepare for the worst (no Google recovery) and hope for the best. Do that by continuing to build the best site you can without regard to what you think that Google may want, because you'll never figure that out ~ that's the whole point of Panda (to be inscrutable).
If you can devote as much time to finding alternatives as you would to pleasing Google (which may be nearly impossible), you'll be laying the groundwork for a stronger longterm recovery. Because as others have found here, you may regain some of your positions in the next week or month or year, only to lose them again the day after. That's a recipe for constant stress ~ I know, I've been there ~ which begs the question: Is Google really worth that?
I think not.