what are the main differences between airport express and extreme?

Here is a product comparison:

http://www.apple.com/wifi/

In addition to Bob Timmons' link the main differences are as follows:

1. Extreme has a slightly more powerful antenna (might not be true but from experience it seems to be)
2. Extreme has USB HDD sharing
3. Express has AirPlay
4. Extreme has 3 Gigabit ports (don't be confused by Apple's page. Apple states 4 including WAN, 3 without WAN)
5. Express is smaller
6. Express has 10/100 Ethernet whereas Extreme has Gigabit