I always thought sending a handwritten thank-you note after a job interview said more than sending a thank-you email.
I was wrong.
When I interviewed for my current job, I had already purchased, addressed, and stamped a $6 card. After I left the interview, I wrote my thanks and immediately slipped it into the mailbox near the office.
I got the job, and, a few months later, was chatted with my coworkers about ways we've tried to impress interviewers throughout our careers. I told them all the ways I had stressed over making sure the note I had sent them was just right. My bosses looked at me blankly.
Turns out they had never received my card.
That's the problem with handwritten letters: They're a nice idea, but they can so easily get lost in the mail. They can take days to arrive. The person you sent the letter to may not check her mailbox everyday. By the time they open and read your card, if they ever do, they may have already hired someone else.
I was lucky but if you rely on a note sent through the mail you may not be.