Academic Poll: Forms of Address

This may be too late in the day to generate much action, but I thought of it just a little while ago. Two questions:

1) If you were writing a letter of recommendation for a student, would you refer to them as “Firstname” or “Mr./Ms. Lastname”?

2) Does your answer depend on the level of the student? That is, would you refer to an undergraduate the same way as a graduate student?

I’ve seen both, and have a definite opinion on the subject, but I’m curious as to what people think.