My letter was mailed on a Wednesday and i received it to Lawrence on a Friday... assuming they mailed your letter yesterday, you may have to wait a little longer.
Also, the acceptance letter was only one page--- so don't panic if you see a thin envelope .... it took me a bit to comprehend that i got in!
Best wishes!!!!
If you don't mind me asking, when did you interview? Was it with the last group? I sure hope that they didn't send out the acceptance letters last week and the rejections this week. That would be very upsetting.