I agree with ckent's comments. If you are interested in a program, by all means, let them know of your interest. Remember that everyone wants to feel wanted and residency programs are no exception.
It is not unusual for program directors to tell applicants that they plan to rank them highly or that "you will definitely match into our program". Many students have gotten themselves in trouble by taking too much stock in this type of statement. You may be flattered by their expression of interest but remember that these words (written or spoken) are not a binding committment.
What has happened in the past is that students have let such comments influence their rank list (either changing the order of their rank list or creating a rank list that is too short). When match time came around, some of these students were surprised to learn that they didn't match at all. To avoid this type of situation, don't base your rank list on any comments you receive from the programs - always base it on the factors that are important to you.
Samir Desai, MD
Assistant Professor of Medicine
Baylor College of Medicine