[t_kozak]

There is kind of interesting project out there: http://www.kickstarter.com/profile/ipen

They seem to use totally different approach - an external motion detector, proximity sensors which gives this tool much better precision. It's this kind of technology as used in kindle touch. Although it's still early for them, idea behind this is quite interesting.

[hristov]

These pens use ultrasound triangulation. I have tried the earlier paper versions of them and they are eerily accurate. I was just thinking someone should use a pen like this for the ipad and it seems that someone already has.