Why does a golf ball have dimples?

Check it out at:

http://www.aerospaceweb.org/question/aerodynamics/

After having sat on a plane for far too many hours in this past year, this extremely well-written website caught my attention a while ago. They answer a lot of those questions that were born from blankly staring at the airplane wing during takeoff/cruise/landing, like "What is that little fin on the engine for?" among other topics. I wish everybody could explain things like these guys. Reading their stuff makes me want to take a class on fluid dynamics. :P

EDIT: http://zikemon.ytmnd.com/