They don't necessarily matter until you hit Twitter-size for performance purposes, but take care to pay close attention to the idea of natural vs. artificial ke

They don't necessarily matter until you hit Twitter-size for performance purposes, but take care to pay close attention to the idea of natural vs. artificial keys, and heed his warning about turning artificial keys into natural keys. One day you'll be integrating database systems together and you'll be glad you followed his advice. I've seen some really ugly bizdata schemas.