I was in Vegas for a couple of days and stopped by the Apple store to check out the ipad. My son picked it up an immediately figure it out. My 4 yr old daughter took about 2 minutes to figure the interface out completely and get games up and running without any of my help. To me that shows Apple (and the other sw developers) got the interface right. An older lady was watching my daughter and was amazed at how fast she could navigate through the options, going from video to game to browser.
To those that think this is just a toy and a touch interface is not the future, I respectfully disagree. Star Trek had it right all those years ago. No, this isn't the perfect gadget for techies, but Apple is smart in targeting the other 99.9% of the population. And sure, this isn't a perfect product but it's a great first gen product. Even though my kids a begging me for one (two actually) I will wait for another version or two first.
Like everyone has said, the display is amazing. Videos were great to watch and some of the games were amazing. The one car racing game were you use the ipad like a steering wheel was our favorite. My son was no longer interested in his Nintendo DS for the trip home.