Jason is running a long comment-thread at his blog about what a seamless user experience might be. What's seamless, he asks... The answers are pretty predictable, and mostly correct.
The thing is, seams are important.
Try throwing a baseball or a football without seams.
Wear clothes without seams and you look like you're on Star Trek.
Seams make it possible to get a grip.
The goal, it seems to me, is not to create things that are seamless. It's to put the seams in places where they are actually useful.