yes, this is something i'm wondering about... also, should the correspondence be sent via email or a more formal letter if anyone has done this or planning to...
I've wondered about this too but more recently have wondered if these letters matter at all? I guess it certainly can't hurt. But when I asked my IM advisor this questions, she told me that most programs pay no attention to the "You're my #1" letter. I don't know how universal this is - buy I know my home institution pays no attention to it.