Yes, waiting is tough.
My son's appointment offer came in a Priority Mail envelope. Stuck in the mailbox just like the other mail. Though the envelope was rigid due to the leather folder the appointment comes in.
No Special Delivery, no Express Mail. Though others have reported getting their appointment by other means.
I do encourage you to stay in touch with your MALO and regional admissions officer. They are your advocate. My son sent a weekly email informing them of any academic, ACT/SAT test scores, or sports developments. Don't be afraid to add items to your file.
He also attended the local USMA info session in October, where he talked to the visiting cadet, his MALO, the region admissions officer, the representative from the local Congressman's office, and another visiting admissions officer who had not been to the area before. Never pass up an opportunity to talk with these people - they are all interested in your interest in attending the USMA.