I got new tires on my Cressida back in November. The old ones were last put on in Dec. 2003 and were starting to crack and not be able to be properly balanced. My new ones were manufactured in the 17th week of 2009.
I think an important thing to do is keep up your tire's maintenance. Rotating the tires, checking the tire pressure periodically, making sure they're properly aligned, etc. will go a long way to ensuring your tire life. Crazy stuff though.