Another Penn admit reporting! Early American. Email from the chair of the history grad group, definitely a form letter with all the basic form letter goodness. I spoke with a POI there last Friday and he implied that they were making all the final decisions this week. I know they interviewed all the Americanists first but I don't know about other fields. Congrats to everyone and good luck! This is a truly hellish process.
As regards the Dr/Professor/Nickname/Lastname debate, I don't think it matters as long as you come across as respectful and mature. What that means varies from person to person and context, but as long as you have the tone right I don't think you need to loose sleep over it. That said, I'd personally never call a professor by their first name until we had a very well established relationship. It took me forever to be ok with calling professors by their first name where I am right now. At my undergrad institution it was very much about Dr. So-and-so and I didn't realize that was considered highly formal until I heard one of my profs complaining about it, haha.
Ps hi! long time lurker, first time poster.