Have you been hit by a manual penalty?
It sometimes feels a little too easy to associate any loss of positioning within Google with the idea that a site has been hit by a penalty. Although this is probably the actual cause in many cases, it's often easy to place blame in the wrong area. If you've been busily submitting reconsideration requests and not getting much joy, then you need to think about your approach. What can a reconsideration request be used for and why...