QSL cards are a time honored tradition in Amateur radio. Final confirmation of the contact, and the basis of most of the "wall paper" awards, especially for the DX'ers.
As a operator of at least semi-exotic callsigns and locations, especially maritime mobile, I pride myself at getting all of the cards I receive answered. While electronic QSL-ing is gaining popularity, there are still many stations who use the old fashion paper cards.
Since regular mail is getting expensive, I have a few rules when you send a card to me, especially directly. I want to return the card to you, but I can't go broke doing so. To help me answer the cards efficiently and economically, you should do the following:
1) look me up in QRZ.com to find out my correct mailing address. Make sure you are QSLing via N1ZZZ not N1ZZ who also goes to locations for DXpeditioning.
2) send a self-addressed envelope. This is very important. I am already going out and having cards printed, I can't be going out and spending more money on envelopes. If you are a US station, paste a "Forever" stamp on the envelope so that if the postage rate increases before I get home to answer they, there won't be a delay or additional cost for me to add postage. Non-US stations should not try to send stamps to me. Also, needing to take the time to fill out the address just adds to my work load.
3) If you are a non-US station, include at least two $1 bills OR an IRC. As of 2012, the cost of an international letter is $1.05. So a single $1 bill means I am paying for your card and at least a bit of your postage. This might not seem like much, but when you have to answer 1,000 cards, the costs add up for me. IRC's are fine because no matter what the cost of the postage, I still get a stamp. I am willing to pay the $0.09 for the card, but at least cover the postage.
4) If you're a US station, don't QSL me via the bureau. It takes forever for me to get the card, and then I have to pay for your card, postage and envelope. This does not make me happy. Take the time to find out my foreign call's manager and send a card directly or electronically.
5) If you don't follow my rules you will probably get a card, but at the very least it will be delayed. I have what is called my "special handling" pile. These are the direct cards with no envelope etc. If you included money or an IRC you will get a direct card, but delayed until every other direct card is answered. This may mean a week or two delay. If you sent no postage or currency, your card will be returned via the bureau.
6) Bureau cards. There are many DX operators who do not answer bureau cards. These not only take the longest, but are also the most expensive for me to answer. I have to front the cost of the card, the cost of the postage from the bureau to me, the cost of the postage to the ARRL bureau, and then the ARRL bureau fee. It is by the sheer sense of duty that I answer bureau cards. While bureau cards are fine for longer ragchew QSO's, when you are working a DX station who is regularly running pilups, you everyone a favor, either use direct paper cards, an EQSL, or nothing at all. If you do insist on a bureau card, be prepared to wait at least a year, usually more for the card to get to me, and then for me to get around to answering them (usually I send my bureau cards out the last week or so before I rejoin the ship) and then for the card to get back to you. In 2012 I am getting many cards from QSO's dating from 2010, and that is only when they get to me. Expect another year or so to get back to you.
So while I am happy to get and return QSL cards, if you want me to get back to you soon so that you can fill out your DXCC paperwork, get LoTW for the fastest response, or send me a card directly so that I can get the card answered reasonably fast.