> Is the whole touchscreen tablet combo worth that premium?
I would say it depends. I love the touch screen (I've disabled my touchpad) - and I love the real pen/digitizer.
The sp4 is basically the dynabook: high dpi screen, a pen that works.
Still some annoyances with scaling in legacy apps - and I've yet to find a great "smart" drawing/cad program that really takes advantage of the pen - I'm thinking something like Ivan Sutherland's "Sketchpad".
I haven't quite gotten around to it, but I believe it would make a great Smalltalk companion (although it's a "button" short). It does work quite well with MIT's "scratch" system.