What's the difference between Blu-ray and HD DVD?

What's the difference between Blu-ray and HD DVD? Sounds like an opening for a joke. Well, it's actually an opening for a fact. 'Blu-ray' is what consumers want."WARNER BROS. ENTERTAINMENT TO RELEASE ITS HIGH-DEFINITION DVD TITLES EXCLUSIVELY IN THE BLU-RAY DISC FORMAT BEGINNING LATER THIS YEAR Decision Made in Response to Strong Consumer Preference for Format."Warner Bros. now joins Disney, Fox