I think it's different depending on the school. So far I've only heard back from Pitt and that was by email, and they sent a letter a few days later.
If you go here http://thegradcafe.com/survey/index.php and type in your school and program of choice it will give you admissions stats for specific people, and it'll also give you an idea of how people are usually notified for that program.
I've skimmed through a bunch of these threads and haven't seen much talk of the Gillings School of Public Health at UNC. Their Health Behavior program is my top choice, but I'm not really sure what my chances are of getting in, or when I'll even find out. They're the number two top PH program in the country so I'm really suprirsed that I haven't heard more about that school.
So who else applied? Has anyone else heard back yet?