I hope everyone watches this video, it's some of the best information I've seen in a long time. In fact, it could save your life!
I checked my new Goodyear's, purchased 5/30/08 and found the date code on two tires (1808, 1108), but the other two were blank where the date code should have been? You can be sure I'll be checking into this!
(The first two digits are the week, the second two are the year of manufacturer.)