if you got fired because you messed up, perhaps an apology letter would be better. if it's a layoff, or a mutual decision, a "thanks for the opportunity and experience" letter would be good. remember - you can't cross a bridge you've burned, and you can't get a good letter of recommendation from a boss you've pissed off.

I have done things like that. I think it earns you much respect. It also feels good to let someone know that what they did doesn't bother you. It's like when someone refuses to help you and then you turn around and help them. It feels good if you are in a decent mood.

No, but I gave a prophetic strangely cordial F U letter that predicted their downfall. And guess what, they're go down in this economy and intend to dance in the ashes!

if it was a job I hated and it give me access to unemployment insurance quicker... Maybe I would.

I might. It would depend on what kind of reference I was getting from the ex-boss. and if I was happy to be free of the company.

I would not send a nasty letter. Someday someone might call there to confirm your employment. The boss can not give their opinion of your work. They might use a tone of voice that conveys a message. You can try and ask for a letter of reference. Say thank you for #years/months of employment - blah blah blah. It can't hurt

Before deciding if you should send a thank you letter, I would ask yourself what your goal is. Do you want to learn more about why you were fired and experience some growth from it; improve yourself? If that's the case, I would do more than a thank-you letter. I would ask the boss for an exit interview and be honest about why. Tell him/her that you'd like to learn from this experience and you value their opinion, "I understand we're not parting on the best of terms, but I'd like to ask you for something. I'd like to learn from this experience as I move on. You're someone who's opinion I value, so would you mind giving me some honest feedback?" If you don't really want to learn about why you were fired--or already know and don't expect any additional insights--but you want to minimize the damage to your personal brand, then there's nothing wrong with a thank you letter. However, I would be clear about what you're thanking him/her for. For example, were there some good things about your relationship? Did you learn things? Did your career advance during the time you were at that job? If so, then you can thank that person for those things. "Although we parted ways on less-than-ideal terms, I understand that our working relationship is more than these past couple weeks and I want to take a moment to thank you for what you've done for me... [insert specifics]... All the best..." There are tons of goals that you might have. These are only a couple examples, of course. Hope that helps. I love talking about these kinds of things. If you do, too, feel free to check out our blog http://socialcapitalmentor.com.