I bought a stylus marketed specifically for the ipad and it sucked. The tip was this big soft spongy foam thing. It was nowhere close to the immediate, reliable experience of putting pen to paper. I was left assuming that the current capacitive technology in these devices is just not up to the task of making pen input work well.
Maybe it can be done easily, but it just wasn't high enough on the priority queue. Maybe Microsoft will do this well with Surface, since it would differentiate them and after all, they were doing tablets with pen input over a decade ago.
Whatever the holdup, I'm still looking forward to tablets that are as easy to write on as pen and paper.