Writing a thesis acknowledgement: should I address the person as "you" or use 3rd person? I'm writing an acknowledgment for my thesis. I looked at several written acknowledgments and realized that the people who are acknowledged are addressed by "you" rather than "He/She". For example, 

"I'm thankful to Dr. Marry. You have been the weekly contact ...." 

But I personally prefer to address them in a 3rd person format saying "She has been the weekly contact".

I'm wondering if my preference is wrong and not common.
I'd go (and did go) with the 3rd person format, for a simple reason: It's not a letter to that one person, nor a (handwritten) dedication/signed copy of a thesis. Instead it is something that is printed and which is (hopefully) read by more than this one person.

So you talk to a broad audience about that person, hence 3rd person. Only if it were a handwritten, personal message in one particular copy, I would ever go with "you".

(Another exception could be a dedication. In contrast to the acknowledgements the dedication is more specific and -- usually -- to one person or specific group of people, like family. In this case 'you' might also make sense, because here you address them personally.)