i remember at my interview joel said that they were hoping to do it through email, but feared the whole sending them out to the wrong bunch scenario, so essentially he wasn't sure yet (or so it seemed.) but hopefully since interviews were done via email, decision letters also will!
LOL I had to laugh because UCSD did this accidentally a few years ago - not for pharm admissions but for undergrad admissions Sent acceptances to not-accepted people by mistake. Just horrible. After I heard about that, from now on I kind of don't take any emails seriously and receiving hard copy really validates it.
Edited to add that I remember hearing about many families who went out to dinner to celebrate just to come back and find out it wasn't real...