I always get a laugh out of why they chose Crocs. For anyone uninformed, see Mike judge quote below:

The wardrobe had to be something that's not around now. It had to be created for a lot of extras, and so you know our wardrobe person was looking for ways to make the budget work. And Crocs were not out in the world yet. They were just a small startup at the time. We shot in 2004, so no one was wearing Crocs. And she showed me these things, and I thought, 'Oh those are great, just stupid plastic shoes. And I said to her, 'But you actually bought these, you can order these. What if by the time the movie comes out, these things are everywhere, and it doesn't look like we're set in the future?' And she said, 'Oh no, that's never going to happen. And sure enough, by the time it comes out two years later, everyone is wearing Crocs. So it already started coming true even faster than we made the movie, really.