The Career Doctor responds:
First, I must offer kudos to you for being so astute to know the value of thank-you letters. Its amazing what a little common courtesy can do to boost your job search. For those of you who have not learned the secret, please read carefully: you really must send thank-you notes or letters to every person you interview with at a prospective employer. Get business cards (or some other method for getting the correct spelling of names and correct titles) and send thank-you letters as soon as possible after the interviews.
I typically favor more formal thank-you letters rather than notes for first interviews. After second interviews, however, where there is obviously good rapport and interest by both parties, I would suggest writing a more informal thank you note, on nice note card paper (rather than standard business paper), in your own handwriting (rather than PC-produced). A handwritten thank you note beyond any content sends a message of connection and fit.
For more information about thank you letters and notes, go to this article on Quintessential Careers: FAQs About Thank You Letters. Follow this link to find some excellent sample thank-you letters.