If you haven't noticed, the recent UO newsletters contained the following paragraph near the button:
It is not clear what they will forgive. But it is more likely you will be unbanned for relatively minor reasons such as harassment, being reported for saying prohibited words like "rape", speedhacking, etc. If you were banned for major exploitation or your account has a note "DO NOT UNBAN UNDER ANY CIRCUMSTANCES EVER" then your chances would be less good.If you have an account that was terminated by CS over a year ago and would like to have it back please contact support (http://uo.com/support-welcome/) and give them the details and identify the account as yours, depending on the termination we will remove the restriction from your account so you may open it again.
But who knows, perhaps the notes were lost and they will unban you no matter how heinous your crimes against Britannia were!
If you are granted amnesty successfully please post a reply here so that other may hear the good news. If you know someone who was banned then let them know they could have another chance.