Being hit with a google penalty is no joke- especially if you depend upon your website for all or part of your income. And even if your website happens to be nothing more than a hobby blog which you don’t plan to monetize, google-penalty issues hurt.
Google penalties ranged in severity from a rankings drop to total de-indexation (like what happened with the Build My Rank network a few months ago). If you suspect that your website has been penalized by Google, then there are three main things that you should do: first, verify that you have indeed been penalized; second, try to get back in Google’s good graces; and third, have a good post-penalization strategy.