The IRS will start accepting returns on Tuesday, January 17, 2012. If you file on the first day, you should expect to receive an acknowledgement no later than Wednesday, January 18th. All returns will show a status of "Awaiting Acceptance" until the IRS accepts the return and sends an acknowledgment which will be forwarded to you.
According to the 2012 IRS e-file Refund Cycle Chart, the first refunds issued will be based on the first transmittal date being January 17th.
Please note that the information in the link above updates each year automatically and will take you to the most recent IRS version of the publication at the time it is accessed.