In response to "How do post cards work?" in my shout box. I'm not sure I understand the question, but I'll try to answer anyway.

First, get a postcard. One from where you have been on vacation, where you go to school (for those in college), or where you live would be great, but not required. It could even just be a blank post card. You can pick up post cards almost anywhere. Even asking your mom, "Mooooooooommmmmm, do we have any post cards?" will often do the trick, as she'll respond with "Yes, honey, let's go find one."

Then write a short message on it with your your username. Something simple like "Hi from blahblah" is sufficient. But you can always write more.

Then put an address on the post card.

AoPS
c/o levans
10865 Rancho Bernardo Rd Ste 100
San Diego, CA 92127

Then put a stamp on the post card.

Then drop it in the mail.

Several days later, the mail delivery person will deliver it to our office. Then dpatrick or tlcruickshank will let me know I have a postcard. Then I'll run downstairs and get the post card. Then I'll get it, put it on my post card board, and thank you on my blog.