I honestly think it doesn't matter. I have about 10 years of professional experience, and while I used to write thank-you e-mails and even snail mail letters on every job interview I went on when I was younger, I stopped doing it a long time ago. Here's why: a) A startup or a mid-sized company will usually act pretty fast in making an offer or informing the candidate they're declined. The bureaucracy at bigger compan…
It can't hurt (much), but it doesn't help much either. As nhashem says, if you want to make a difference, do it in the interview itself. That's what counts, not the old school advice of a thank you note, an objective statement, or heavyweight paper.