There has been quite a ripple effect from the latest Panda update. I myself have had one of my sideline affiliate websites hit slightly, (only by about 25% so I actually feel quite lucky).
Anyway, I have been referring to a couple of sources for the recovery operation.
Forbes have released a helpful guide on how to diagnose and recover from 4.1. You can find it here
There's also an unofficial webmaster guide on the sites.google.com URL - Head here for that
It really is about pulling your sleeves up, pruning your sites for any bad wood in the way of thin content. Make sure that the site is working efficiently overall, (no bad links, slow page speeds, needs to be responsive) and that the user's interests come first. And of course, going forward only great content.
Unfortunately, even after you've made all the necessary changes, it could still be some time before you see your site performing as it was before.