I participated in the give-one-get-one program and got one of these for my kids (6 and 8). I literally pulled it out of the box, put in the batteries, showed them where to plug in the power cord, and have not touched it since. Two days after getting it, my six year old had written multiple stories and was browsing the web easily enough that I'll need to think about watching where they go browsing. She'd also figured out how to use the microphone and the camera software and was using them somewhat ... creatively (you need to think like a 6-year old...).
Based on this, I'd say the interface is pretty good. They're still getting used to the transactions for pulling up the stories they've written, but other than that it's been very smooth.