I got one too ... interviewed in December. So, do you think it is a "we really like you in particular" kind of letter or just letting everyone know they've recruited more faculty?
I looked into it and they have not had their meeting to rank applicants yet, therefore probably means nothing, especially since 4 people on here have it.
I received one as well.
The letter itself seemed pretty generic, but mine had a hand-written note at the bottom. I'm not sure that helps to solve the mystery...