You do. If you want the job, that is.

The thank you letter is a critical element of the interviewing process. In a way, it's analogous to the defense attorney making his closing summation at trial. The evidence has been presented; now he's wrapping the whole thing up with a bow, recapping what's been said, and trying to convince the jury why they should decide in his client's favor. It's not uncommon for the case to be won or lost on the basis of the summation.

If you're the person on trial, you probably don't want your attorney to phone this in. Or to decide it isn't worth doing at all - why not skip it and roll the dice? Let's just send them in to deliberations and let the chips fall where they may. After all, this is just a formality, right?

Yeah, I don't think so.

Likewise, this thank you is a closing summation of sorts - and equally important. You're recapping the interview and everything that's happened up to this point and trying to convince them to hire you. This letter is your final opportunity to reiterate your unique selling proposition and make a lasting impression. It's your last chance to restate the most important aspects of your candidacy and summarize how you can help the company meet its challenges.

That means you give this some thought and craft a persuasive, error free letter. Everyone you interviewed with gets one. No copies - each person gets his or her own letter.

Skip this step (or fail to take it seriously) at your peril.