IMHO a real letter ALWAYS looks better. It gives a better impression, and suggests that you care more.
Showing up for your interview in scrubs after a shift is easy too, but nobody does that (Well actually I did see one applicant who did that, he also refused the free lunch because all of his questions had been answered and he "wasn't hungry").
After spending hundreds of hours debating, traveling and agonizing, as well as thousands of dollars, is it really such a big deal to take 10 minutes and 39cents to send a real letter.
My wife made me send letters (to every person I interviewed with, the PD and the program coordinator--- don't forget the coordinator), and I think it made a difference. After I got in the coordinator told me that it showed my level of interest, and made a definate impression on the selection committee.
I know time and money are short, but make the extra effort, especially to programs you really like.