I am also facing similar situation, but I don't know the reason of Penalty.. such that I can correct and ask google to have another look on my site...
on 21st I have lost rank for nearly all my keyword.. Those keyword which were on top 3 were thrown to 41st Position... It was the clear indication that we have been penalized...
Some Fact:
> We have taken some sponsord links which had the
PR of 6.. but they have lost their
PR.. to 0 ( May be Penalized )... Does this could me also...
As I never linked them... ?
> Some of my link exchange Page
PR has gone down to zero.. MAY be this could be the reason of Penalty...
What should i do to get out of this penalty...