Thanks Yesitsme! The status update for my case on Dec 18th also indicated that my petition was approved. May be you could carefully re-check the current status of your case (https://egov.uscis.gov/cris/Dashboard/CaseStatus.do). Good luck!
The following is the text from my case status update on Dec 18th:
"Application Type: I140, IMMIGRANT PETITION FOR ALIEN WORKER
Your Case Status: Decision
On December 18, 2012, your I140, IMMIGRANT PETITION FOR ALIEN WORKER was approved. You will be notified of the decision by mail. Please check our website at www.uscis.gov for further updates on your case, including when the approval notice is mailed. If you do not receive the approval notice within 30 days, please call customer service at 1-800-375-5283 for further assistance.
During this step the formal decision (approved/denied) is written and the decision notice is mailed and/or emailed to the applicant/petitioner. You can use our current processing time to gauge when you can expect to receive a final decision.
If you have questions or concerns about your application or the case status results listed above, or if you have not received a decision from USCIS within the current processing time listed*, please contact USCIS Customer Service at (800) 375-5283.
*Current processing times can be found on the USCIS website at www.uscis.gov under Check Processing Times."