Did you friend get a job promotion?
Have a baby?
Getting a vacation to Korea?
Make sure you say, "Chukha hamnida!"
It's probably one of the least "everyday" useful Korean phrases I've learned, but I think it's my favorite! I've found plenty of occasions to use it, and people are always delighted.
This Howcast video teaches you how to congratulate someone in Korean. The romanization is a little different from the standard (which I used above), but it is actually more helpful in terms of pronunciation. You learned a new phrase! Chukha hamnida!